Thermal Flow Meter with a Case Having a Resin Housing which Supports a Circuit Package

ABSTRACT

Provided is a thermal flow meter to improve the measurement accuracy of a temperature detector provided in a thermal flow meter is a thermal flow meter to improve the measurement accuracy of a temperature detector provided in a thermal flow meter. The thermal flow meter includes a bypass passage through which a measurement target gas  30  flowing through a main passage flows, and a circuit package  400  which includes a measurement circuit for measuring a flow rate of the measurement target gas  30  flowing through the bypass passage and a temperature detecting portion  452  for detecting a temperature of the measurement target gas. The circuit package  400  includes a circuit package body which is molded by a resin to internally envelope the measurement circuit and a protrusion  424  molded by the resin. The temperature detecting portion  452  is provided in the leading end portion of the protrusion  424,  and at least the leading end portion of the protrusion protrudes to the outside from a housing  302.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/407,169, filed Dec. 11, 2014, which claims priority fromInternational Application No. PCT/JP2013/063476, filed May 15, 2013,which claims priority from Japanese Patent Application No. 2012-135305,filed Jun. 15, 2012, the disclosures of which are expressly incorporatedby reference herein.

TECHNICAL FIELD

The present invention relates to a thermal flow meter.

BACKGROUND ART

A flow rate of a gas is measured, a temperature of the gas is measured,and the flow rate and the temperature of the gas thus measured are usedas parameters to perform control. In this way, the control accuracy canbe improved by using the measured temperature of the gas in addition tothe measured flow rate of the gas for control. For example, in thecontrol of an internal combustion engine used for driving a vehicle, thecontrol accuracy is improved by using a temperature of an intake air ismeasured in addition to the intake air guided to the internal combustionengine in order to calculate a fuel supply amount of the internalcombustion engine or an ignition timing. A thermal flow meter formeasuring the flow rate of the gas and an intake air temperature sensorfor measuring a temperature of the gas are separately provided, andwiring lines are respectively used for the measurement. However, thereis a known technology in which the thermal flow meter and the intake airtemperature sensor are combined into one measurement device, forexample, an internal combustion engine in which these components areprovide in an intake pipe. The measurement device includes two circuitsof the thermal flow meter and the intake air temperature sensor, theflow rate of the gas is measured by the thermal flow meter, and thetemperature of the intake air is detected by the intake air temperaturesensor which is attached in the thermal flow meter. Such a technology isdisclosed, for example, JP 2008-209243 A.

CITATION LIST Patent Literature

PLT 1: JP 2008-209243 A

SUMMARY OF INVENTION Technical Problem

In the technology disclosed in PLT 1, the detection elements fordetecting the flow rate of the gas and the temperature of the gas areseparately arranged, and the respective elements are electricallyconnected to each other in the measurement target gas. However, thearrangement in such a state of the respective elements connected in themeasurement target gas may cause various problems while maintainingreliability. It is difficult to maintain the reliability and measurementaccuracy at a high level for detecting the temperature simply byproviding a flow meter for measuring the flow rate and a temperaturesensor for measuring the temperature of the gas into one device. It ispreferable to obtain the high measurement accuracy for the temperaturedetection while securing the reliability.

The present invention has been made to provide a thermal flow meterwhich can maintain the reliability in the temperature detection anddetect a temperature with high measurement accuracy, and includes a gastemperature detecting portion.

Solution to Problem

A thermal flow meter according to the invention to solve the aboveproblem includes a bypass passage into which a measurement target gasflowing through a main passage flows, a circuit package which includes ameasurement circuit for measuring a flow rate by performing heattransfer with the measurement target gas flowing through the bypasspassage and a temperature detecting portion for detecting a temperatureof the measurement target gas, and a case which includes an externalterminal for outputting an electric signal representing the flow rateand an electric signal representing a temperature of the measurementtarget gas and supports the circuit package. The case includes a resinhousing which supports the circuit package. The circuit package isconfigured to envelope the measurement circuit and the temperaturedetecting portion with a resin. The temperature detecting portionincludes a protrusion protruding from a circuit package body. At leastthe leading end portion of the protrusion protrudes to the outside fromthe housing.

Furthermore, a thermal flow meter includes a bypass passage into which ameasurement target gas flowing through a main passage flows, a circuitpackage which includes a measurement circuit for measuring a flow rateby performing heat transfer with the measurement target gas flowingthrough the bypass passage and a temperature detecting portion fordetecting a temperature of the measurement target gas, and a case whichincludes an external terminal for outputting an electric signalrepresenting the flow rate and an electric signal representing atemperature of the measurement target gas and supports the circuitpackage. The case includes a resin housing which supports the circuitpackage. The housing includes a first housing having the bypass passageand a second housing positioned on a side near the flange from the firsthousing. An air passage is provided between the first housing and thesecond housing to flow the measurement target gas flowing through themain passage. The circuit package includes a circuit package body whichis molded by a resin to internally envelope the measurement circuit anda protrusion molded by the resin. The temperature detecting portion isprovided in the leading end portion of the protrusion, and at least theleading end portion of the protrusion protrudes to the outside from ahousing. The opening of the air passage provided between the firsthousing and the second housing is provided at a position of theprotrusion.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a thermalflow meter which can maintain the reliability in temperature detectionand detect a temperature with high measurement accuracy, and includes agas temperature detecting portion.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system diagram illustrating an internal combustion enginecontrol system where a thermal flow meter according to an embodiment ofthe invention is used.

FIGS. 2A and 2B are diagrams illustrating an appearance of the thermalflow meter, in which FIG. 2A is a left side view, and FIG. 2B is a frontview.

FIGS. 3A and 3B are diagrams illustrating an appearance of the thermalflow meter, in which FIG. 3A is a right side view, and FIG. 3B is a rearview.

FIGS. 4A and 4B are diagrams illustrating an appearance of the thermalflow meter, in which FIG. 4A is a plan view, and FIG. 4B is a bottomview.

FIGS. 5A and 5B are diagrams illustrating a housing of the thermal flowmeter, in which FIG. 5A is a left side view of the housing, and FIG. 5Bis a front view of the housing.

FIGS. 6A and 6B are diagrams illustrating a housing of the thermal flowmeter, in which FIG. 6A is a right side view of the housing, and FIG. 6Bis a rear view of the housing.

FIG. 7 is a partially enlarged view illustrating a state of a flow pathsurface arranged in the bypass passage.

FIGS. 8A to 8C are diagrams illustrating an appearance of a front cover,in which FIG. 8A is a left side view, FIG. 8B is a front view, and FIG.8C is a plan view.

FIGS. 9A to 9C are diagrams illustrating an appearance of a rear cover304, in which FIG. 9A is a left side view, FIG. 9B is a front view, andFIG. 9C is a plan view.

FIG. 10 is a partially enlarged view of a terminal connector.

FIGS. 11A to 11C are exterior views illustrating a circuit package, inwhich FIG. 11A is a left side view, FIG. 11B is a front view, and FIG.11C is a rear view.

FIG. 12 is a diagram illustrating a state that circuit components aremounted on a frame of the circuit package.

FIG. 13 is an explanatory diagram illustrating a diaphragm and a linkchannel that connects an opening and a gap inside the diaphragm.

FIG. 14 is a diagram illustrating a condition of the circuit packageafter a first resin molding process.

FIGS. 15A and 15B are diagrams illustrating another embodiment of thecircuit package of FIGS. 11A to 11C, in which FIG. 15A is a front viewof the circuit package, and FIG. 15B is a rear view.

FIG. 16 is a diagram illustrating an overview of the manufacturingprocess of the circuit package.

FIG. 17 is a diagram illustrating an overview of a manufacturing processof the thermal flow meter.

FIG. 18 is a diagram illustrating an overview of another embodiment ofthe manufacturing process of the thermal flow meter.

FIG. 19 is a circuit diagram illustrating a flow rate detection circuitof the thermal flow meter.

FIG. 20 is an explanatory diagram for describing an air flow sensingportion of the flow rate detection circuit.

FIG. 21 is a front view illustrating another embodiment of the housingwhich includes the thermal flow meter.

FIG. 22 is a diagram illustrating another embodiment of detecting atemperature of a measurement target gas.

FIG. 23 is a diagram illustrating another embodiment of a temperaturedetecting portion.

DESCRIPTION OF EMBODIMENTS

Examples for embodying the invention described below (hereinafter,referred to as embodiments) solves various problems desired as apractical product. In particular, the embodiments solve various problemsfor use in a measurement device for measuring an intake air amount of avehicle and exhibit various effects. One of various problems addressedby the following embodiments is described in the “Problems to Be Solvedby the Invention” described above, and one of various effects obtainedby the following embodiments is described in the “Effects of theInvention.” Various problems solved by the following embodiments andvarious effects obtained the following embodiments will be furtherdescribed in the “Description of Embodiments.” Therefore, it would beappreciated that the following embodiments also include other effects orproblems obtained or addressed by the embodiments than those describedin “Problems to Be Solved by the Invention” or “Effects of theInvention.”

In the following embodiments, like reference numerals denote likeelements even when they are inserted in different drawings, and theyhave the same functional effects. The components that have beendescribed in previous paragraphs may not be described by denotingreference numerals and signs in the drawings.

1. Internal Combustion Engine Control System Having Thermal Flow MeterAccording to One Embodiment of the Invention

FIG. 1 is a system diagram illustrating an electronic fuel injectiontype internal combustion engine control system having a thermal flowmeter according to one embodiment of the invention. Based on theoperation of an internal combustion engine 110 having an engine cylinder112 and an engine piston 114, an intake air as a measurement target gas30 is inhaled from an air cleaner 122 and is guided to a combustionchamber of the engine cylinder 112 through a main passage 124 including,for example, an intake body, a throttle body 126, and an intake manifold128. A flow rate of the measurement target gas 30 as an intake airguided to the combustion chamber is measured by a thermal flow meter 300according to the invention. A fuel is supplied from a fuel injectionvalve 152 based on the measured flow rate and is mixed with the intakeair, so that the mixed gas is guided to the combustion chamber. It isnoted that, in this embodiment, the fuel injection valve 152 is providedin an intake port of the internal combustion engine, and the fuelinjected to the intake port is mixed with the measurement target gas 30as an intake air to form a mixed gas, so that the mixed gas is guided tothe combustion chamber through an inlet valve 116 to generate mechanicalenergy by burning.

In recent years, in many vehicles, a direct fuel injection method havingexcellent effects in exhaust gas purification or fuel efficiencyimprovement is employed, in which a fuel injection valve 152 isinstalled in a cylinder head of the internal combustion engine, and fuelis directly injected into each combustion chamber from the fuelinjection valve 152. The thermal flow meter 300 may be similarly used ina type in which fuel is directly injected into each combustion chamberas well as a type in which fuel is injected into the intake port of theinternal combustion engine of FIG. 1. A method of measuring controlparameters, including a method of using the thermal flow meter 300, anda method of controlling the internal combustion engine, including a fuelsupply amount or an ignition timing, are similar in basic conceptbetween both types. A representative example of both types, a type inwhich fuel is injected into the intake port is illustrated in FIG. 1.

The fuel and the air guided to the combustion chamber have a fuel/airmixed state and are explosively combusted by spark ignition of theignition plug 154 to generate mechanical energy. The gas aftercombustion is guided to an exhaust pipe from the exhaust valve 118 andis discharged to the outside of the vehicle from the exhaust pipe as anexhaust gas 24. The flow rate of the measurement target gas 30 as anintake air guided to the combustion chamber is controlled by thethrottle valve 132 of which opening level changes in response tomanipulation of an accelerator pedal. The fuel supply amount iscontrolled based on the flow rate of the intake air guided to thecombustion chamber, and a driver controls an opening level of thethrottle valve 132, so that the flow rate of the intake air guided tothe combustion chamber is controlled. As a result, it is possible tocontrol mechanical energy generated by the internal combustion engine.

1.1 Overview of Control of Internal Combustion Engine Control System

The flow rate and the temperature of the measurement target gas 30 as anintake air that is received from the air cleaner 122 and flows throughthe main passage 124 are measured by the thermal flow meter 300, and anelectric signal representing the flow rate and the temperature of theintake air is input to the control device 200 from the thermal flowmeter 300. In addition, an output of the throttle angle sensor 144 thatmeasures an opening level of the throttle valve 132 is input to thecontrol device 200, and an output of a rotation angle sensor 146 isinput to the control device 200 to measure a position or a condition ofthe engine piston 114, the inlet valve 116, or the exhaust valve 118 ofthe internal combustion engine and a rotational speed of the internalcombustion engine. In order to measure a mixed ratio state between thefuel amount and the air amount from the condition of exhaust gas 24, anoutput of an oxygen sensor 148 is input to the control device 200.

The control device 200 computes a fuel injection amount or an ignitiontiming based on a flow rate of the intake air as an output of thethermal flow meter 300 and a rotational speed of the internal combustionengine measured from an output of the rotation angle sensor 146. Basedon the computation result of them, a fuel amount supplied from the fuelinjection valve 152 and an ignition timing for igniting the ignitionplug 154 are controlled. In practice, the fuel supply amount or theignition timing is further accurately controlled based on a change ofthe intake temperature or the throttle angle measured by the thermalflow meter 300, a change of the engine rotation speed, and an air-fuelratio state measured by the oxygen sensor 148. In the idle driving stateof the internal combustion engine, the control device 200 furthercontrols the air amount bypassing the throttle valve 132 using an idleair control valve 156 and controls a rotation speed of the internalcombustion engine under the idle driving state.

1.2 Improvement of Measurement Accuracy of Thermal Flow Meter havingTemperature Detecting Function of Intake Air and Environment forMounting Thermal Flow Meter

Both of the fuel supply amount and the ignition timing as main controlamounts of the internal combustion engine are calculated using theoutput of the thermal flow meter 300 as a main parameter. In addition, acontrol parameter is calibrated based on a temperature of the intake airas needed. Improvement of measurement accuracy, suppression of aging,and improvement of reliability in the thermal flow meter 300 areimportant for improvement of control accuracy of a vehicle or obtainmentof reliability. In particular, in recent years, there are a lot ofdemands for fuel saving of the vehicle and exhaust gas purification. Inorder to satisfy such demands, it is significantly important to improvethe measurement accuracy of the flow rate of the intake air which ismeasured by the thermal flow meter 300. In addition, it is alsoimportant to maintain a high reliability of the thermal flow meter 300.

A vehicle having the thermal flow meter 300 is used under an environmentwhere a temperature change is significant or a coarse weather such as astorm or snow. When a vehicle travels a snowy road, it travels through aroad on which an anti-freezing agent is sprayed. It is preferable thatthe thermal flow meter 300 be designed considering a countermeasure forthe temperature change or a countermeasure for dust or pollutants undersuch a use environment. Furthermore, the thermal flow meter 300 isinstalled under an environment where the internal combustion engine issubjected to vibration. It is also desired to maintain high reliabilityfor vibration.

The thermal flow meter 300 is installed in the intake pipe influenced byheat from the internal combustion engine. For this reason, the heatgenerated from the internal combustion engine is transferred to thethermal flow meter 300 via the intake pipe which is a main passage 124.Since the thermal flow meter 300 measures the flow rate of themeasurement target gas by transferring heat with the measurement targetgas, it is important to suppress influence of the heat from the outsideas much as possible.

The thermal flow meter 300 mounted on a vehicle solves the problemsdescribed in “Problems to Be Solved by the Invention” and provides theeffects described in “Effects of the Invention” as described below. Inaddition, as described below, it solves various problems demanded as aproduct and provides various effects considering various problemsdescribed above. Specific problems or effects solved or provided by thethermal flow meter 300 will be described in the following description ofembodiments.

2. Configuration of Thermal Flow Meter 300

2.1 Exterior Structure of Thermal Flow Meter 300

FIGS. 2(A), 2(B), 3(A), 3(B), 4(A), and 4(B) are diagrams illustratingan appearance of the thermal flow meter 300, in which FIG. 2(A) is aleft side view of the thermal flow meter 300, FIG. 2(B) is a front view,FIG. 3(A) is a right side view, FIG. 3(B) is a rear view, FIG. 4(A) is aplan view, and FIG. 4(B) is a bottom view. The thermal flow meter 300includes a case 301. The case 301 includes a housing 302, a front cover303, and a rear cover 304. The housing 302 includes a flange 312 whichfixes the thermal flow meter 300 to an intake body as a main passage124, an external connector 305 which has external terminals 306 formaking electrical connection with an external device, and a measuringportion 310 which measures a flow rate. The measuring portion 310 isinternally provided with a bypass passage trench for making a bypasspassage. Further, the measuring portion 310 includes a circuit package400. The circuit package 400 includes an air flow sensing portion 602(refer to FIG. 19) which measures the flow rate of the measurementtarget gas 30 flowing through the main passage 124 and a temperaturedetecting portion 452 which measures a temperature of the measurementtarget gas 30 flowing through the main passage 124.

2.2 Effects Based on Exterior Structure of Thermal Flow Meter 300

Since the inlet port 350 of the thermal flow meter 300 is provided inthe leading end side of the measuring portion 310 extending toward thecenter direction of the main passage 124 from the flange 312, the gas inthe vicinity of the center portion distant from the inner wall surfaceinstead of the vicinity of the inner wall surface of the main passage124 may be input to the bypass passage. For this reason, the thermalflow meter 300 can measure a flow rate or a temperature of the airdistant from the inner wall surface of the main passage 124 of thethermal flow meter 300, so that it is possible to suppress a decrease ofthe measurement accuracy caused by influence of heat and the like. Inthe vicinity of the inner wall surface of the main passage 124, thethermal flow meter 300 is easily influenced by the temperature of themain passage 124, so that the temperature of the measurement target gas30 has a different condition from an original temperature of the gas andexhibits a condition different from an average condition of the main gasinside the main passage 124. In particular, if the main passage 124serves as an intake body of the engine, it may be influenced by the heatfrom the engine and remains in a high temperature. For this reason, thegas in the vicinity of the inner wall surface of the main passage 124has a temperature higher than the original temperature of the mainpassage 124 in many cases, so that this degrades the measurementaccuracy.

In the vicinity of the inner wall surface of the main passage 124, afluid resistance increases, and a flow velocity decreases, compared toan average flow velocity in the main passage 124. For this reason, ifthe gas in the vicinity of the inner wall surface of the main passage124 is input to the bypass passage as the measurement target gas 30, adecrease of the flow velocity against the average flow velocity in themain passage 124 may generate a measurement error. In the thermal flowmeter 300 illustrated in FIGS. 2(A), 2(B), 3(A), 3(B), and 4(A) to 4(C),since the inlet port 350 is provided in the leading end of the thin andlong measuring portion 310 extending to the center of the main passage124 from the flange 312, it is possible to reduce a measurement errorrelating to a decrease of the flow velocity in the vicinity of the innerwall surface. In the thermal flow meter 300 illustrated in FIGS. 2(A),2(B), 3(A), 3(B), and 4(A) to 4(C), in addition to the inlet port 350provided in the leading end of the measuring portion 310 extending tothe center of the main passage 124 from the flange 312, an outlet portof the bypass passage is also provided in the leading end of themeasuring portion 310. Therefore, it is possible to further reduce themeasurement error.

The measuring portion 310 of the thermal flow meter 300 has a shapeextending from the flange 312 to the center direction of the mainpassage 124, and its leading end is provided with the inlet port 350 forinputting a part of the measurement target gas 30 such as an intake airto the bypass passage and the outlet port 352 for returning themeasurement target gas 30 from the bypass passage to the main passage124. While the measuring portion 310 has a shape extending along an axisdirected to the center from the outer wall of the main passage 124, itswidth has a narrow shape as illustrated in FIG. 2(A) or 3(A). That is,the measuring portion 310 of the thermal flow meter 300 has a frontsurface having an approximately rectangular shape and a side surfacehaving a thin width. As a result, the thermal flow meter 300 can have abypass passage having a sufficient length, and it is possible tosuppress a fluid resistance to a small value for the measurement targetgas 30. For this reason, using the thermal flow meter 300, it ispossible to suppress the fluid resistance to a small value and measurethe flow rate of the measurement target gas 30 with high accuracy.

2.3 Structure and Effects of Measuring Portion 310

An upstream-side protrusion 317 and a downstream-side protrusion 318 areprovided in the upstream-side side surface and the downstream-side sidesurface, respectively, of the measuring portion 310 included in thethermal flow meter 300. The upstream-side protrusion 317 and thedownstream-side protrusion 318 have a shape narrowed along the leadingend to the base, so that it is possible to reduce a fluid resistance ofthe measurement target gas 30 as an intake air flowing through the mainpassage 124. The upstream-side protrusion 317 is provided between thethermal insulation 315 and the inlet port 343. The upstream-sideprotrusion 317 has a large cross section and receives a large heatconduction from the flange 312 or the thermal insulation 315. However,the upstream-side protrusion 317 is cut near the inlet port 343, and alength of the temperature detecting portion 452 from the temperaturedetecting portion 452 of the upstream-side protrusion 317 increases dueto the hollow of the upstream-side outer wall of the housing 302 asdescribed below. For this reason, the heat conduction is suppressed fromthe thermal insulation 315 to the support portion of the temperaturedetecting portion 452.

In addition, a terminal connector 320 and a gap including the terminalconnector 320 described below are formed between the flange 312 or thethermal insulation 315 and the temperature detecting portion 452. Forthis reason, a distance between the flange 312 or the thermal insulation315 and the temperature detecting portion 452 becomes long, and thefront cover 303 or the rear cover 304 is provided in this long portionwhich serves as a cooling surface. Therefore, it is possible to reducean influence of the temperature of the wall surface of the main passage124 onto the temperature detecting portion 452. In addition, since thedistance between the flange 312 or the thermal insulation 315 and thetemperature detecting portion 452 becomes long, it is possible to guidethe measurement target gas 30 input to the bypass passage in thevicinity of the center of the main passage 124. It is possible tosuppress a decrease of the measurement accuracy concerned with the wallsurface of the main passage 124.

As illustrated in FIG. 2(B) or 3(B), both side surfaces of the measuringportion 310 inserted into the main passage 124 have a very narrow shape,and a leading end of the downstream-side protrusion 318 or theupstream-side protrusion 317 has a narrow shape relative to the basewhere the air resistance is reduced. For this reason, it is possible tosuppress an increase of the fluid resistance caused by insertion of thethermal flow meter 300 into the main passage 124. Furthermore, in theportion where the downstream-side protrusion 318 or the upstream-sideprotrusion 317 is provided, the upstream-side protrusion 317 or thedownstream-side protrusion 318 protrudes toward both sides relative toboth side portions of the front cover 303 or the rear cover 304. Sincethe upstream-side protrusion 317 or the downstream-side protrusion 318is formed of a resin molding, they are easily formed in a shape havingan insignificant air resistance. Meanwhile, the front cover 303 or therear cover 304 is shaped to have a wide cooling surface. For thisreason, the thermal flow meter 300 has a reduced air resistance and canbe easily cooled by the measurement target air flowing through the mainpassage 124.

2.4 Structure and Effects of Flange 312

The flange 312 is provided with a plurality of hollows 314 on its lowersurface which is a portion facing the main passage 124, so as to reducea heat transfer surface with the main passage 124 and make it difficultfor the thermal flow meter 300 to receive influence of the heat. Thescrew hole 313 of the flange 312 is provided to fix the thermal flowmeter 300 to the main passage 124, and a space is formed between asurface facing the main passage 124 around each screw hole 313 and themain passage 124 such that the surface facing the main passage 124around the screw hole 313 recedes from the main passage 124. As aresult, the flange 312 has a structure capable of reducing heat transferfrom the main passage 124 to the thermal flow meter 300 and preventingdegradation of the measurement accuracy caused by heat. Furthermore, inaddition to the heat conduction reduction effect, the hollow 314 canreduce influence of contraction of the resin of the flange 312 duringthe formation of the housing 302.

The thermal insulation 315 is provided in the measuring portion 310 sideof the flange 312. The measuring portion 310 of the thermal flow meter300 is inserted into the inside from an installation hole provided inthe main passage 124 so that the thermal insulation 315 faces the innersurface of the installation hole of the main passage 124. The mainpassage 124 serves as, for example, an intake body, and is maintained ata high temperature in many cases. Conversely, it is conceived that themain passage 124 is maintained at a significantly low temperature whenthe operation is activated in a cold district. If such a high or lowtemperature condition of the main passage 124 affects the temperaturedetecting portion 452 or the measurement of the flow rate describedbelow, the measurement accuracy is degraded. For this reason, aplurality of hollows 316 are provided side by side in the thermalinsulation 315 adjacent to the hole inner surface of the main passage124, and a width of the thermal insulation 315 adjacent to the holeinner surface between the neighboring hollows 316 is significantly thin,which is equal to or smaller than ⅓ of the width of the fluid flowdirection of the hollow 316. As a result, it is possible to reduceinfluence of temperature. In addition, a portion of the thermalinsulation 315 becomes thick. During a resin molding of the housing 302,when the resin is cooled from a high temperature to a low temperatureand is solidified, volumetric shrinkage occurs so that a deformation isgenerated as a stress occurs. By forming the hollow 316 in the thermalinsulation 315, it is possible to more uniformize the volumetricshrinkage and reduce stress concentration.

The measuring portion 310 of the thermal flow meter 300 is inserted intothe inside from the installation hole provided in the main passage 124and is fixed to the main passage 124 using the flange 312 of the thermalflow meter 300 with screws. The thermal flow meter 300 is preferablyfixed to the installation hole provided in the main passage 124 with apredetermined positional relationship. The hollow 314 provided in theflange 312 may be used to determine a positional relationship betweenthe main passage 124 and the thermal flow meter 300. By forming theconvex portion in the main passage 124, it is possible to provide aninsertion relationship between the convex portion and the hollow 314 andfix the thermal flow meter 300 to the main passage 124 in an accurateposition.

2.5 Structures and Effects of External Connector 305 and Flange 312

FIG. 4(A) is a plan view illustrating the thermal flow meter 300. Fourexternal terminal 306 and a calibration terminal 307 are provided insidethe external connector 305. The external terminals 306 include terminalsfor outputting the flow rate and the temperature as a measurement resultof the thermal flow meter 300 and a power terminal for supplying DCpower for operating the thermal flow meter 300. The calibration terminal307 is used to measures the produced thermal flow meter 300 to obtain acalibration value of each thermal flow meter 300 and store thecalibration value in an internal memory of the thermal flow meter 300.In the subsequent measurement operation of the thermal flow meter 300,the calibration data representing the calibration value stored in thememory is used, and the calibration terminal 307 is not used. Therefore,in order to prevent the calibration terminal 307 from hinderingconnection between the external terminals 306 and other externaldevices, the calibration terminal 307 has a shape different from that ofthe external terminal 306. In this embodiment, since the calibrationterminal 307 is shorter than the external terminal 306, the calibrationterminal 307 does not hinder connection even when the connectionterminal connected to the external terminal 306 for connection toexternal devices is inserted into the external connector 305. Inaddition, since a plurality of hollows 308 are provided along theexternal terminal 306 inside the external connector 305, the hollows 308reduce stress concentration caused by shrinkage of resin when the resinas a material of the flange 312 is cooled and solidified.

Since the calibration terminal 307 is provided in addition to theexternal terminal 306 used during the measurement operation of thethermal flow meter 300, it is possible to measure characteristics ofeach thermal flow meter 300 before shipping to obtain a variation of theproduct and store a calibration value for reducing the variation in theinternal memory of the thermal flow meter 300. The calibration terminal307 is formed in a shape different from that of the external terminal306 in order to prevent the calibration terminal 307 from hinderingconnection between the external terminal 306 and external devices afterthe calibration value setting process. In this manner, using the thermalflow meter 300, it is possible to reduce a variation of each thermalflow meter 300 before shipping and improve measurement accuracy.

3. Entire Structure of Housing 302 and Its Effects

3.1 Structures and Effects of Bypass Passage and Air Flow SensingPortion

FIGS. 5(A), 5(B), 6(A), and 6(B) illustrate a state of the housing 302when the front and rear covers 303 and 304 are removed from the thermalflow meter 300. FIG. 5(A) is a left side view illustrating the housing302, FIG. 5(B) is a front view illustrating the housing 302, FIG. 6(A)is a right side view illustrating the housing 302, and FIG. 6(B) is arear view illustrating the housing 302. In the housing 302, themeasuring portion 310 extends from the flange 312 to the centerdirection of the main passage 124, and a bypass passage trench forforming the bypass passage is provided in its leading end side. In thisembodiment, the bypass passage trench is provided on both frontside andbackside of the housing 302. FIG. 5(B) illustrates a bypass passagetrench on frontside 332, and FIG. 6(B) illustrates a bypass passagetrench on backside 334. Since an inlet trench 351 for forming the inletport 350 of the bypass passage and an outlet trench 353 for forming theoutlet port 352 are provided in the leading end of the housing 302, thegas distant from the inner wall surface of the main passage 124, thatis, the gas flow through the vicinity of the center of the main passage124 can be received as the measurement target gas 30 from the inlet port350. The gas flowing through the vicinity of the inner wall surface ofthe main passage 124 is influenced by the temperature of the wallsurface of the main passage 124 and has a temperature different from theaverage temperature of the gas flowing through the main passage 124 suchas the intake air in many cases. In addition, the gas flowing throughthe vicinity of the inner wall surface of the main passage 124 has aflow velocity lower than the average flow velocity of the gas flowingthrough the main passage 124 in many cases. Since the thermal flow meter300 according to the embodiment is resistant to such influence, it ispossible to suppress a decrease of the measurement accuracy.

The bypass passage formed by the bypass passage trench on frontside 332or the bypass passage trench on backside 334 described above isconnecter to the thermal insulation 315 through the outer wall hollowportion 366, the upstream-side outer wall 335, or the downstream-sideouter wall 336. In addition, the upstream-side outer wall 335 isprovided with the upstream-side protrusion 317, and the downstream-sideouter wall 336 is provided with the downstream-side protrusion 318. Inthis structure, since the thermal flow meter 300 is fixed to the mainpassage 124 using the flange 312, the measuring portion 310 having thecircuit package 400 is fixed to the main passage 124 with highreliability.

In this embodiment, the housing 302 is provided with the bypass passagetrench for forming the bypass passage, and the covers are installed onthe frontside and backside of the housing 302, so that the bypasspassage is formed by the bypass passage trench and the covers. In thisstructure, it is possible to form overall bypass passage trenches as apart of the housing 302 in the resin molding process of the housing 302.In addition, since the dies are provided in both surfaces of the housing302 during formation of the housing 302, it is possible to form both thebypass passage trench on frontside 332 and bypass passage trench onbackside 334 as a part of the housing 302 by using the dies for both thesurfaces. Since the front and rear covers 303 and 304 are provided inboth the surfaces of the housing 302, it is possible to obtain thebypass passages in both surfaces of the housing 302. Since the front andbypass passage trench on frontside 332 and bypass passage trenches onbackside 334 are formed on both the surfaces of the housing 302 usingthe dies, it is possible to form the bypass passage with high accuracyand obtain high productivity.

In FIG. 6(B), a part of the measurement target gas 30 flowing throughthe main passage 124 is input to the inside of the bypass passage trenchon backside 334 from the inlet trench 351 that forms the inlet port 350,and flows through the bypass passage trench on backside 334. The bypasspassage trench on backside 334 gradually deepens as it goes inside, andthe measurement target gas 30 slowly moves to the front direction as itflows along the trench. In particular, the bypass passage trench onbackside 334 is provided with a steep slope portion 347 that steeplydeepens at the front side of a hole 342, so that a part of the airhaving a light mass moves along the steep slope portion 347 and thenflows to the side of a measurement surface 430 illustrated in FIG. 5(B)from the hole 342. Meanwhile, since a foreign object having a heavy masshas difficulty in steeply changing its path, the foreign object moves tothe side of a backside of measurement surface 431 illustrated in FIG.6(B). Then, the foreign object flows to the measurement surface 430illustrated in FIG. 5(B) through a hole 341.

In the bypass passage trench on frontside 332 of FIG. 5(B), the air as ameasurement target gas 30 moving from the hole 342 to the bypass passagetrench on frontside 332 side flows along the measurement surface 430,and heat transfer is performed with the air flow sensing portion 602 formeasuring a flow rate using the heat transfer surface exposing portion436 provided in the measurement surface 430 in order to measure a flowrate. Both the measurement target gas 30 passing through the measurementsurface 430 or the air flowing from the hole 341 to the bypass passagetrench on frontside 332 flow along the bypass passage trench onfrontside 332 and are discharged from the outlet trench 353 for formingthe outlet port 352 to the main passage 124.

A substance having a heavy mass such as a contaminant mixed in themeasurement target gas 30 has a high inertial force and has difficultyin steeply changing its path to the deep side of the trench along thesurface of the steep slope portion 347 of FIG. 6(B) where a depth of thetrench steeply deepens. For this reason, since a foreign object having aheavy mass moves through the side of the backside of measurement surface431, it is possible to suppress the foreign object from passing throughthe vicinity of the heat transfer surface exposing portion 436. In thisembodiment, since most of foreign objects having a heavy mass other thanthe gas pass through the backside of measurement surface 431 which is arear surface of the measurement surface 430, it is possible to reduceinfluence of contamination caused by a foreign object such as an oilcomponent, carbon, or a contaminant and suppress degradation of themeasurement accuracy. That is, since the path of the measurement targetgas 30 steeply changes along an axis across the flow axis of the mainpassage 124, it is possible to reduce influence of a foreign objectmixed in the measurement target gas 30.

In this embodiment, the flow path including the bypass passage trench onbackside 334 is directed to the flange from the leading end of thehousing 302 along a curved line, and the gas flowing through the bypasspassage in the side closest to the flange flows reversely to the flow ofthe main passage 124, so that the bypass passage in the rear surfaceside as one side of this reverse flow is connected to the bypass passageformed in the front surface side as the other side. As a result, it ispossible to easily fix the heat transfer surface exposing portion 436 ofthe circuit package 400 to the bypass passage and easily receive themeasurement target gas 30 in the position close to the center of themain passage 124.

In the embodiment, the hole 342 and the hole 341 are provided on thefront and backsides in a flow direction of the measurement surface 430for measuring the flow rate to penetrate the bypass passage trench onbackside 334 and the bypass passage trench on frontside 332. Using thehole 342 and the hole 341 provided to penetrate the bypass passagetrench, the bypass passage is molded such that the measurement targetgas 30 moves from the bypass passage trench on backside 334 molded inone surface of the housing 302 to the bypass passage trench on frontside332 molded in the other surface of the housing 302. With thisconfiguration, it is possible to mold the bypass passage trenches onboth surfaces of the housing 302 through a single resin molding processalong a structure for connecting the both surfaces.

In addition, since the hole 342 and the hole 341 are provided on bothsides of the measurement surface 430 molded in the circuit package 400,it is possible to prevent an inflow of the resin into the heat transfersurface exposing portion 436 molded in the measurement surface 430 byusing dies for molding the hole 342 and the hole 341 on the both sides.In addition, since the hole 342 and the hole 341 are molded on theupstream side and on the downstream side of the measurement surface 430,when the circuit package 400 is fixed to the housing 302 by the resinmolding process, the dies are arranged using these holes, so that thecircuit package 400 can be positioned and fixed by the dies.

In the embodiment, two holes (the hole 342 and the hole 341) areprovided as the holes penetrating the bypass passage trench on backside334 and the bypass passage trench on frontside 332. However, even whenthe two holes including the hole 342 and the hole 341 are not provided,in a case where any one of the holes is used, it is possible to form thestructure of the bypass passage connecting the bypass passage trench onbackside 334 and the bypass passage trench on frontside 332 by thesingle resin molding process.

Further, an inside wall of bypass passage on backside 391 and an outsidewall of bypass passage on backside 392 are provided on both sides of thebypass passage trench on backside 334, and the inner side surface of therear cover 304 abuts on the leading end portion in the height directionof each of the inside wall of bypass passage on backside 391 and theoutside wall of bypass passage on backside 392, so that the bypasspassage on backside of the housing 302 is molded. In addition, an insidewall of bypass passage on frontside 393 and an outside wall of bypasspassage on frontside 394 are provided on both sides of the bypasspassage trench on frontside 332, and the inner side surface of the rearcover 304 abuts on the leading end portion in the height direction ofeach of the inside wall of bypass passage on frontside 393 and theoutside wall of bypass passage on frontside 394, so that the bypasspassage on frontside of the housing 302 is molded.

In this embodiment, the measurement target gas 30 dividingly flowsthrough the measurement surface 430 and its rear surface, and the heattransfer surface exposing portion 436 for measuring the flow rate isprovided in one of them. However, the measurement target gas 30 may passthrough only the surface side of the measurement surface 430 instead ofdividing the measurement target gas 30 into two passages. By curving thebypass passage to follow a second axis across a first axis of the flowdirection of the main passage 124, it is possible to gather a foreignobject mixed in the measurement target gas 30 to the side where thecurve of the second axis is insignificant. By providing the measurementsurface 430 and the heat transfer surface exposing portion 436 in theside where the curve of the second axis is significant, it is possibleto reduce influence of a foreign object.

In this embodiment, the measurement surface 430 and the heat transfersurface exposing portion 436 are provided in a link portion between thebypass passage trench on frontside 332 and the bypass passage trench onbackside 334. However, the measurement surface 430 and the heat transfersurface exposing portion 436 may be provided in the bypass passagetrench on frontside 332 or the bypass passage trench on backside 334instead of the link portion between the bypass passage trench onfrontside 332 and the bypass passage trench on backside 334.

An orifice shape is formed in a part of the heat transfer surfaceexposing portion 436 provided in the measurement surface 430 to measurea flow rate, so that the flow velocity increases due to the orificeeffect, and the measurement accuracy is improved. In addition, even if avortex is generated in a flow of the gas in the upstream side of theheat transfer surface exposing portion 436, it is possible to eliminateor reduce the vortex using the orifice and improve measurement accuracy.

Referring to FIGS. 5(A), 5(B), 6(A), and 6(B), an outer wall hollowportion 366 is provided, where the upstream-side outer wall 335 has ahollow shape hollowed to the downstream side in a neck portion of thetemperature detecting portion 452. Due to this outer wall hollow portion366, a distance between the temperature detecting portion 452 and theouter wall hollow portion 366 increases, so that it is possible toreduce influence of the heat transferred via the upstream-side outerwall 335.

Although the circuit package 400 is enveloped by the fixing portion 372for fixation of the circuit package 400, it is possible to increase aforce for fixing the circuit package 400 by further fixing the circuitpackage 400 using the outer wall hollow portion 366. The fixing portion372 envelopes the circuit package 400 along a flow axis of themeasurement target gas 30. Meanwhile, the outer wall hollow portion 366envelops the circuit package 400 across the flow axis of the measurementtarget gas 30. That is, the circuit package 400 is enveloped such thatthe enveloping direction is different with respect to the fixing portion372. Since the circuit package 400 is enveloped along the two differentdirections, the fixing force is increased. Although the outer wallhollow portion 366 is a part of the upstream-side outer wall 335, thecircuit package 400 may be enveloped in a direction different from thatof the fixing portion 372 using the downstream-side outer wall 336instead of the upstream-side outer wall 335 in order to increase thefixing force. For example, a plate portion of the circuit package 400may be enveloped by the downstream-side outer wall 336, or the circuitpackage 400 may be enveloped using a hollow hollowed in the upstreamdirection or a protrusion protruding to the upstream direction providedin the downstream-side outer wall 336. Since the outer wall hollowportion 366 is provided in the upstream-side outer wall 335 to envelopthe circuit package 400, it is possible to provide an effect ofincreasing a thermal resistance between the temperature detectingportion 452 and the upstream-side outer wall 335 in addition to fixationof the circuit package 400.

Since the outer wall hollow portion 366 is provided in a neck portion ofthe temperature detecting portion 452, it is possible to reduceinfluence of the heat transferred from the flange 312 or the thermalinsulation 315 through the upstream-side outer wall 335. Furthermore, atemperature measurement hollow 368 formed by a notch between theupstream-side protrusion 317 and the temperature detecting portion 452is provided. Using the temperature measurement hollow 368, it ispossible to reduce heat transfer to the temperature detecting portion452 through the upstream-side protrusion 317. As a result, it ispossible to improve detection accuracy of the temperature detectingportion 452. In particular, since the upstream-side protrusion 317 has alarge cross section, it easily transfers heat, and a functionality ofthe temperature measurement hollow 368 that suppress heat transferbecomes important.

3.2 Structure and Effects of Air Flow Sensing Portion of Bypass Passage

FIGS. 7(A) and 7(B) are partially enlarged views illustrating a statethat the surface 430 of the circuit package 400 is arranged inside thebypass passage trench as a cross-sectional view taken along the line A-Aof FIGS. 6(A) and 6(B). It is noted that FIGS. 7(A) and 7(B) are aconceptual diagram omitted and simplified compared to the specificconfiguration of FIGS. 5(A), 5(B), 6(A), and 6(B), and details maybeslightly modified. The left side of FIGS. 7(A) and 7(B) is a terminatedend portion of the bypass passage trench on backside 334, and the rightside is a starting end portion of the bypass passage trench on frontside332. Although not illustrated clearly in FIGS. 7(A) and 7(B), the hole342 and the hole 341 are provided in both the left and right sides ofthe circuit package 400 having the measurement surface 430, and thebypass passage trench on backside 334 and the bypass passage trench onfrontside 332 are connected to the left and right sides of the circuitpackage 400 having the measurement surface 430.

The measurement target gas 30 that is received from the inlet port 350and flows through the bypass passage on backside including the bypasspassage trench on backside 334 is guided from the left side of FIG. 7. Apart of the measurement target gas 30 flows to a flow path 386 includingthe front side of the measurement surface 430 of the circuit package 400and a protrusion 356 provided in the front cover 303 through the hole342. The other measurement target gas 30 flows to a flow path 387 formedby the backside of measurement surface 431 and the rear cover 304. Then,the measurement target gas 30 flowing through the flow path 387 moves tothe bypass passage trench on frontside 332 through the hole 341 and iscombined with the measurement target gas 30 flowing through the flowpath 386, so that it flows through the bypass passage trench onfrontside 332 and is discharged from the outlet port 352 to the mainpassage 124. Further, the protrusion 358 provided in the rear cover 304protrudes to the backside of measurement surface 431 in the flow path387.

Since the bypass passage trench is molded such that the measurementtarget gas 30 guided from the bypass passage trench on backside 334 tothe flow path 386 through the hole 342 passes through the flow pathcurved wider than that guiding to the flow path 387, a substance havinga heavy mass such as a contaminant contained in the measurement targetgas 30 is gathered in the flow path 387 being less curved. For thisreason, there is nearly no flow of the foreign object into the flow path386.

The flow path 386 is structured to have an orifice molded such that thefront cover 303 is provided successively to the leading end portion ofthe bypass passage trench on frontside 332, and the protrusion 356smoothly protrudes to the measurement surface 430 side. The measurementsurface 430 is arranged in one side of the orifice portion of the flowpath 386 and is provided with the heat transfer surface exposing portion436 for performing heat transfer between the air flow sensing portion602 and the measurement target gas 30. In order to perform measurementof the air flow sensing portion 602 with high accuracy, the measurementtarget gas 30 in the heat transfer surface exposing portion 436preferably makes a laminar flow having a little vortex. In addition,with the flow velocity being faster, the measurement accuracy is moreimproved. For this reason, the orifice is molded such that theprotrusion 356 provided in the front cover 303 to face the measurementsurface 430 smoothly protrudes to the measurement surface 430. Thisorifice reduces a vortex in the measurement target gas 30 to approximatethe flow to a laminar flow. Furthermore, since the flow velocityincreases in the orifice portion, and the heat transfer surface exposingportion 436 for measuring the flow rate is arranged in the orificeportion, the measurement accuracy of the flow rate is improved.

Since the orifice is molded such that the protrusion 356 protrudes tothe inside of the bypass passage trench to face the heat transfersurface exposing portion 436 provided on the flow passage surface 430,it is possible to improve measurement accuracy. The protrusion 356 formolding the orifice is provided on the cover facing the heat transfersurface exposing portion 436 provided on the flow passage surface 430.In FIG. 7, since the cover facing the heat transfer surface exposingportion 436 provided on the flow passage surface 430 is the front cover303, the heat transfer surface exposing portion 436 is provided in thefront cover 303. Alternatively, the heat transfer surface exposingportion 436 may also be provided in the cover facing the heat transfersurface exposing portion 436 provided on the flow passage surface 430 ofthe front or rear cover 303 or 304. Depending on which of the surfacesis provided with the flow passage surface 430 and the heat transfersurface exposing portion 436 in the circuit package 400, the cover thatfaces the heat transfer surface exposing portion 436 is changed.

A distribution of the measurement target gas 30 between the flow paths386 and 387 also relates to the high accuracy measurement. Adistribution of the measurement target gas 30 between the flow paths 386and 387 may be adjusted by causing the protrusion 358 provided in therear cover 304 to protrude to the flow path 387. In addition, since theorifice portion is provided in the flow path 387, it is possible toincrease the flow velocity and guide a foreign object such as acontaminant to the flow path 387. In the embodiment, the orifice formedby the protrusion 358 is used as one of means for adjustment between theflow paths 386 and 387. Alternatively, the aforementioned distributionof the flow rate between the flow paths 386 and 387 may be adjusted byadjusting a width between the backside of measurement surface 431 andthe rear cover 304 and the like. In this case, the protrusion 358provided in the rear cover 304 is not necessary.

Referring to FIGS. 5(A), 5(B), 6(A), and 6(B), a press imprint 442 ofthe die used in the resin molding process for the circuit package 400remains on the backside of measurement surface 431 as a rear surface ofthe heat transfer surface exposing portion 436 provided on themeasurement surface 430. The press imprint 442 does not particularlyhinder the measurement of the flow rate and does not make any problemeven when the press imprint 442 remains. In addition, as describedbelow, it is important to protect a semiconductor diaphragm of the airflow sensing portion 602 when the circuit package 400 is molded throughresin molding. For this reason, pressing of the rear surface of the heattransfer surface exposing portion 436 is important. Furthermore, it isvery important to prevent resin that covers the circuit package 400 fromflowing to the heat transfer surface exposing portion 436. For thisviewpoint, the inflow of the resin is suppressed by enveloping themeasurement surface 430 including the heat transfer surface exposingportion 436 using a die and pressing the rear surface of the heattransfer surface exposing portion 436 using another die. Since thecircuit package 400 is made through transfer molding, a pressure of theresin is high, and pressing from the rear surface of the heat transfersurface exposing portion 436 is important. In addition, since asemiconductor diaphragm is used in the air flow sensing portion 602, aventilation passage for a gap created by the semiconductor diaphragm ispreferably molded. In order to hold and fix a plate and the like formolding the ventilation passage, pressing from the rear surface of theheat transfer surface exposing portion 436 is important.

3.3 Shapes and Effects of Front and Rear Covers 303 and 304

FIGS. 8(A) to 8(C) are diagrams illustrating an appearance of the frontcover 303, in which FIG. 8(A) is a left side view, FIG. 8(B) is a frontview, and FIG. 8(C) is a plan view. FIGS. 9(A) and 9(B) are diagramsillustrating an appearance of the rear cover 304, in which FIG. 9(A) isa left side view, FIG. 9(B) is a front view, and FIG. 9(C) is a planview. In FIGS. 8(A), 8(B), 8(C), 9(A), 9(B), and 9(C), the front or rearcover 303 or 304 is used to form the bypass passage by covering thebypass passage trench of the housing 302. In addition, the front or rearcover 303 or 304 is used to provide an orifice provided in theprotrusion 356. For this reason, it is preferable to increase moldingaccuracy. Since the front or rear cover 303 or 304 is formed through aresin molding process by injecting a thermoplastic resin into a die, itis possible to form the front or rear cover 303 or 304 with high moldingaccuracy.

The front protection portion 322 or the rear protection portion 325 isformed in the front or rear cover 303 or 304 illustrated in FIGS. 8(A)to 8(C) or 9(A) to 9(C). As illustrated in FIG. 2(A), 2(B), 3(A), or3(B), the front protection portion 322 provided in the front cover 303is arranged on the front side surface of the inlet port 343, and therear protection portion 325 provided in the rear cover 304 is arrangedin the back side surface of the inlet port 343. The temperaturedetecting portion 452 arranged inside the inlet port 343 is protected bythe front protection portion 322 and the rear protection portion 325, sothat it is possible to prevent a mechanical damage of the temperaturedetecting portion 452 caused when the temperature detecting portion 452collides with something during production or loading on a vehicle.

The inner side surface of the front cover 303 is provided with theprotrusion 356. As illustrated in FIGS. 7(A) and 7(B), the protrusion356 is arranged to face the measurement surface 430 and has a shapeextending along an axis of the flow path of the bypass passage. Anorifice is formed in the flow path 386 described above using themeasurement surface 430 and the protrusion 356 so as to reduce a vortexgenerated in the measurement target gas 30 and generate a laminar flow.In this embodiment, the bypass flow path having the orifice portion isdivided into a trench portion and a lid portion that covers the trenchto form a flow path having an orifice, and the trench portion is formedthrough a second resin molding process for forming the housing 302.Then, the front cover 303 having the protrusion 356 is formed throughanother resin molding process, and the trench is covered by using thefront cover 303 as a lid of the trench to form the bypass passage. Inthe second resin molding process for forming the housing 302, thecircuit package 400 having the measurement surface 430 is also fixed tothe housing 302. Since formation of the trench having such a complicatedshape is performed through a resin molding process, and a protrusion 356for the orifice is provided in the front cover 303, it is possible toform the flow path 386 of FIGS. 7(A) and 7(B) with high accuracy. Inaddition, since an arrangement relationship between the trench and themeasurement surface 430 or the heat transfer surface exposing portion436 can be maintained with high accuracy, it is possible to reduce avariation of the product and as a result obtain a high measurementresult. Therefore, it is possible to improve productivity.

This is similarly applied to the molding of the flow path 387 using therear cover 304 and the backside of measurement surface 431. The flowpath 386 is divided into a trench portion and a lid portion. The trenchportion is formed through the second resin molding process in which thehousing 302 is molded. Then, the flow path 387 is molded to cover thetrench using the rear cover 304 having the protrusion 358. By formingthe flow path 387 in this manner, it is possible to form the flow path386 with high accuracy and also improve productivity. Further, althoughthe orifice is provided in the flow path 387 in this embodiment, theflow path 387 having no orifice may be used without using the protrusion358.

In FIG. 8(B), a notch 323 for molding the outlet port 352 is provided onthe leading end side of the front cover 303. As illustrated in FIG.2(B), the outlet port 352 is widened on the front surface side of thehousing 302 from the notch 323 as well as the right surface of thehousing 302. With this configuration, the fluid resistance of the entirebypass passage is reduced, the measurement target gas 30 guided from theinlet port 350 into the bypass passage is increased. Therefore, themeasurement accuracy of the flow rate is improved.

3.4 Structure and Effects of Terminal Connector 320

FIG. 10 is an enlarged view of the terminal connector 320 of the housing302 illustrated in FIGS. 5(A), 5(B), 6(A), and 6(B). However, adifference from the description of FIGS. 5(A), 5(B), 6(A), and 6(B) isas follows. Specifically, in FIGS. 5(A), 5(B), 6(A), and 6(B), the innersockets of external terminals 361 are separated from each other.However, FIG. 10 illustrates the respective inner sockets of externalterminals 361 which are not separated yet, and respective the innersockets of external terminals 361 are connected to each other through alink portion 365. The inner sockets of external terminals 361 protrudingto the circuit package 400 of the external terminal 306 are overlappedwith connection terminals 412, or close to the connection terminals 412,and then each external terminal 306 is fixed to the housing 302 throughresin molding in a second molding process. In order to preventdeformation or a deviation of arrangement of each external terminal 306,according to an embodiment, the external terminal 306 is fixed to thehousing 302 by the resin molding process (the second resin moldingprocess) for molding the housing 302 in a state where the inner socketsof external terminals 361 are connected to each other through the linkportion 365. Alternatively, the external terminal 306 may be fixed tothe housing 302 by the second molding process after the connectionterminal 412 and the inner sockets of external terminals 361 are fixed.

3.5 Inspection of Finished Product through First Resin Molding Process

In the embodiment of FIG. 10, the number of terminals provided in thecircuit package 400 is larger than the number of inner sockets ofexternal terminals 361. Out of the terminals of the circuit package 400,each of the connection terminals 412 is connected to each of the innersockets of external terminals 361, and the terminals 414 are notconnected to the inner sockets of external terminals 361. That is,although the terminals 414 are provided in the circuit package 400, theyare not connected to the inner sockets of external terminals 361.

In FIG. 10, in addition to the connection terminal 412 connected to theinner socket of external terminal 361, the terminal 414 not connected tothe inner socket of external terminal 361 is provided. After the circuitpackage 400 is produced through the first resin molding process, it isinspected whether or not the circuit package 400 is appropriatelyoperated, and whether or not an abnormality in electrical connection isgenerated in the first resin molding process. As a result, it ispossible to maintain high reliability for each circuit package 400. Theterminal 414 not connected to the inner socket of external terminal 361is used in such an inspection of the circuit package 400. Since theterminal 414 is not used after the inspection work, these unusedterminals 414 may be cut out at the base of the circuit package 400after the inspection or maybe buried in the resin serving as theterminal side fixing portion 362 as illustrated in FIG. 10. By providingthe terminal 414 not connected to the inner socket of external terminal361 in this manner, it is possible to inspect whether or not anabnormality is generated in the circuit package 400 produced through thefirst resin molding process and maintain high reliability.

3.6 Communication Structure Between Gap Inside Housing 302 and Outsideof Thermal Flow Meter 300

As illustrated in the partially enlarged view of FIG. 10, a hole 364 isprovided in the housing 302. The hole 364 is connected to the opening309 provided in the inside of the external connector 305 illustrated inFIG. 4(A). According to the embodiment, both sides of the housing 302are sealed with the front and rear covers 303 and 304. If the hole 364is not provided, a difference is generated between the air pressureinside the gap and the atmospheric air pressure due to a temperaturechange of the air inside the gap including the terminal connector 320.It is preferable to reduce such a pressure difference. For this reason,the hole 364 connected to the opening 309 provided in the inside of theexternal connector 305 is provided inside the gap of the housing 302.The external connector 305 has structure resistant to an adverse effectof water and the like in order to improve reliability in electricalconnection. By providing the opening 309 inside the external connector305, it is possible to prevent intrusion of water and a foreign objectsuch as a contaminant or dust from the opening 309.

4. Structure for Fixing Circuit Package 400 Using Housing 302

4.1 Structure for Fixing Circuit Package 400 Using Fixing Portion ofHousing 302

Next, fixation of the circuit package 400 to the housing 302 through aresin molding process will be described again with reference to FIGS.5(A), 5(B), 6(A), and 6(B). The circuit package 400 is arranged in andfixed to the housing 302 such that the measurement surface 430 formed onthe front surface of the circuit package 400 is arranged in apredetermined position of the bypass passage trench for forming thebypass passage, for example, a link portion between the bypass passagetrench on frontside 332 and the bypass passage trench on backside 334 inthe embodiment of FIGS. 5(A), 5(B), 6(A), and 6(B). A portion forburying and fixing the circuit package 400 into the housing 302 througha resin molding is provided as a fixing portion 372 for burying andfixing the circuit package 400 into the housing 302 in the side slightlycloser to the flange 312 from the bypass passage trench. The fixingportion 372 is buried so as to cover the outer circumference of thecircuit package 400 formed through the first resin molding process.

As illustrated in FIG. 5(B), a hollow 376 and a hollow 378 are providedin the front surface of the fixing portion 372. In addition, asillustrated in FIG. 6(B), a hollow 373 is molded in the rear surface ofthe fixing portion 372. With these hollows, it is possible to alleviatecontraction caused when a temperature of the resin is cooled duringmolding of the fixing portion 372, and to reduce a stress concentrationapplied to the circuit package 400. Furthermore, by limiting the flow ofthe resin using the die for molding the hollow, a speed of reduction intemperature of the resin is alleviated and it is possible to easily makethe resin of the fixing portion 372 flow to the inside of unevennessprovided in the surface of the circuit package 400.

The entire surface of the circuit package 400 is not covered by a resinused to form the housing 302, but a portion where the outer wall of thecircuit package 400 is exposed is provided in the flange 312 side of thefixing portion 372. In the embodiment of FIGS. 5(A), 5(B), 6(A), and6(B), the area of a portion exposed from the resin of the housing 302but not enveloped by the housing 302 is larger than the area of aportion enveloped by the resin of the housing 302 out of the outercircumferential surface of the circuit package 400. Furthermore, aportion of the measurement surface 430 of the circuit package 400 isalso exposed from the resin of the housing 302.

Since the circumference of the circuit package 400 is enveloped in thesecond resin molding process for forming the housing 302 by molding thehollows in the front surface and the rear surface of the fixing portion372 that envelopes the outer wall of the circuit package 400 across theentire circumference in a thin band shape, it is possible to alleviatean excessive stress concentration caused by volume contraction in thecourse of solidification of the fixing portion 372. The excessive stressconcentration may adversely affect the circuit package 400.

4.2 Improvement of Adherence of Housing 302 and Circuit Package 400

In order to more robustly fix the circuit package 400 with a small areaby reducing the area of a portion enveloped by the resin of the housing302 of the outer circumferential surface of the circuit package 400, itis preferable to increase adherence of the circuit package 400 to theouter wall in the fixing portion 372. When a thermoplastic resin is usedto form the housing 302, it is preferable that the thermoplastic resinbe penetrated into fine unevennesses on the outer wall of the circuitpackage 400 while it has low viscosity, and the thermoplastic resin besolidified while it is penetrated into the fine unevennesses of theouter wall. In the resin molding process for forming the housing 302, itis preferable that the inlet port of the thermoplastic resin be providedin the fixing portion 372 and in the vicinity thereof. The viscosity ofthe thermoplastic resin increases as the temperature decreases, so thatit is solidified. Therefore, by flowing the thermoplastic resin having ahigh temperature into the fixing portion 372 or from the vicinitythereof, it is possible to solidify the thermoplastic resin having lowviscosity while it abuts on the outer wall of the circuit package 400.In addition, by molding the hollow 376, the hollow 378, and the hollow373 to the fixing portion 372, an obstacle portion for limiting the flowof thermoplastic resin is formed using the die for making these hollows,and thus a movement speed of the thermoplastic resin in the fixingportion 372 is reduced. As a result, a temperature decrease of thethermoplastic resin is suppressed, and a low viscosity state ismaintained, so that adherence between the circuit package 400 and thefixing portion 372 is improved.

By roughening the outer wall surface of the circuit package 400, it ispossible to improve adherence between the circuit package 400 and thefixing portion 372. As a method of roughening the outer wall surface ofthe circuit package 400, there is known a roughening method for formingfine unevennesses on the surface of the circuit package 400, such as asatin-finish treatment, after forming the circuit package 400 throughthe first resin molding process. As the roughening method for formingfine unevennesses on the surface of the circuit package 400, forexample, the roughening may be achieved using sand blasting.Furthermore, the roughening may be achieved through a laser machining.

As another roughening method, an uneven sheet is attached on an innersurface of the die used in the first resin molding process, and theresin is pressed to the die having the sheet on the surface. Even usingthis method, it is possible to form and roughen fine unevennesses on asurface of the circuit package 400. Alternatively, unevennesses may beattached on an inner side of the die for forming the circuit package 400to roughen the surface of the circuit package 400. The surface portionof the circuit package 400 for such roughening is at least a portionwhere the fixing portion 372 is provided. In addition, the adherence isfurther strengthened by roughening a surface portion of the circuitpackage 400 where the outer wall hollow portion 366 is provided.

When the unevenness machining is performed for the surface of thecircuit package 400 using the aforementioned sheet, the depth of thetrench depends on the thickness of the sheet. If the thickness of thesheet increases, the molding of the first resin molding process becomesdifficult, so that the thickness of the sheet has a limitation. If thethickness of the sheet decreases, the depth of the unevenness providedon the sheet in advance has a limitation. For this reason, when theaforementioned sheet is used, it is preferable that the depth of theunevenness between the bottom and the top of the unevenness be set to 10μm or larger and 20 μm or smaller. In the depth smaller than 10 μm, theadherence effect is degraded. The depth larger than 20 μm is difficultto obtain from the aforementioned thickness of the sheet.

In roughening methods other than the aforementioned method of using thesheet, it is preferable to set a thickness of the resin in the firstresin molding process for forming the circuit package 400 to 2 mm orsmaller. For this reason, it is difficult to increase the depth of theunevenness between the bottom and the top of the unevenness to 1 mm orlarger. Conceptually, it is anticipated that adherence between the resinthat covers the circuit package 400 and the resin used to form thehousing 302 increases as the depth of the unevenness between the bottomand the top of the unevenness on the surface of the circuit package 400increases. However, for the reason described above, the depth of theunevenness between the bottom and the top of the unevenness ispreferably set to 1 mm or smaller. That is, if the unevenness having athickness of 10 μm or larger and 1 mm or smaller is provided on thesurface of the circuit package 400, it is preferable to increaseadherence between the resin that covers the circuit package 400 and theresin used to form the housing 302.

A thermal expansion coefficient is different between the thermosettingresin used to mold the circuit package 400 and the thermoplastic resinused to mold the housing 302 having the fixing portion 372. It ispreferable to prevent an excessive stress generated from this differenceof the thermal expansion coefficient from being applied to the circuitpackage 400. With the hollow 373, the hollow 378, and the hollow 376, itis possible to reduce the stress applied to the circuit package 400.

By forming the fixing portion 372 that envelops the outer circumferenceof the circuit package 400 in a band shape and narrowing the width ofthe band, it is possible to alleviate a stress caused by a difference ofthe thermal expansion coefficient applied to the circuit package 400. Awidth of the band of the fixing portion 372 is set to 10 mm or smaller,and preferably 8 mm or smaller. In this embodiment, since the outer wallhollow portion 366 as a part of the upstream-side outer wall 335 of thehousing 302 as well as the fixing portion 372 envelops the circuitpackage 400 to fix the circuit package 400, it is possible to furtherreduce the width of the band of the fixing portion 372. The circuitpackage 400 can be fixed, for example, if the width is set to 3 mm orlarger.

In order to reduce a stress caused by the difference of the thermalexpansion coefficient, a portion covered by the resin used to form thehousing 302 and an exposed portion without covering are provided on thesurface of the circuit package 400. A plurality of portions where thesurface of the circuit package 400 is exposed from the resin of thehousing 302 are provided, and one of them is to the measurement surface430 having the heat transfer surface exposing portion 436 describedabove. In addition, a portion exposed to a part of the flange 312 siderelative to the fixing portion 372 is provided. Furthermore, the outerwall hollow portion 366 is formed to expose a portion of the upstreamside relative to the outer wall hollow portion 366, and this exposedportion serves as a support portion that supports the temperaturedetecting portion 452. A gap is formed such that a portion of the outersurface of the circuit package 400 in the flange 312 side relative tothe fixing portion 372 surrounds the circuit package 400 across itsouter circumference, particularly, the side facing the flange 312 fromthe downstream side of the circuit package 400 and further across theupstream side of the portion close to the terminal of the circuitpackage 400. Since the gap is formed around the portion where thesurface of the circuit package 400 is exposed, it is possible to reducethe heat amount transferred to the circuit package 400 through theflange 312 from the main passage 124 and suppress degradation ofmeasurement accuracy caused by the heat.

A gap is formed between the circuit package 400 and the flange 312, andthis gap serves as a terminal connector 320. The connection terminal 412of the circuit package 400 and the inner socket of external terminal 361positioned in the housing 302 side of the external terminal 306 areelectrically connected to each other using this terminal connector 320through spot welding, laser welding, and the like. The gap of theterminal connector 320 can suppress heat transfer from the housing 302to the circuit package 400 as described above and is provided as a spacethat can be used to perform a connection work between the connectionterminal 412 of the circuit package 400 and the inner socket of externalterminal 361 of the external terminal 306.

4.3 Molding of Housing 302 through Second Resin Molding Process andImprovement in Measurement Accuracy

In the housing 302 illustrated in FIGS. 5(A), 5(B), 6(A), and 6(B)described above, the circuit package 400 having the air flow sensingportion 602 or the processing unit 604 is manufactured through the firstresin molding process. Then, the housing 302 having, for example, thebypass passage trench on frontside 332 or the bypass passage trench onbackside 334 for forming the bypass passage where the measurement targetgas 30 flows are manufactured through the second resin molding process.Through this second resin molding process, the circuit package 400 isembedded into the resin of the housing 302 and is fixed to the inside ofthe housing 302 through resin molding. As a result, the air flow sensingportion 602 performs heat transfer with the measurement target gas 30,so that a configuration relationship such as a positional relationshipor a directional relationship between the heat transfer surface exposingportion 436 for measuring the flow rate and the bypass passageincluding, for example, the bypass passage trench on frontside 332 orthe bypass passage trench on backside 334 can be maintained withremarkably high accuracy. In addition, it is possible to suppress anerror or deviation generated in each circuit package 400 to a very smallvalue. As a result, it is possible to remarkably improve measurementaccuracy of the circuit package 400. For example, compared to aconventional method in which fixation is performed using an adhesive, itis possible to improve measurement accuracy twice or more. Since thethermal flow meter 300 is typically manufactured in large quantities,the method of using an adhesive along with strict measurement has alimitation in improvement of measurement accuracy. However, if thecircuit package 400 is manufactured through the first resin moldingprocess as in this embodiment, and the bypass passage is then formed inthe second resin molding process for forming the bypass passage wherethe measurement target gas 30 flows while the circuit package 400 andthe bypass passage are fixed, it is possible to remarkably reduce avariation of the measurement accuracy and remarkably improve themeasurement accuracy of each thermal flow meter 300. This similarlyapplies to the embodiment of FIG. 7 as well as the embodiment of FIG. 5or 6.

Further referring to the embodiment of, for example, FIGS. 5(A), 5(B),6(A), or 6(B), it is possible to fix the circuit package 400 to thehousing 302 such that a relationship between the bypass passage trenchon frontside 332, the bypass passage trench on backside 334, and theheat transfer surface exposing portion 436 is set to a specificrelationship. As a result, in each of the thermal flow meters 300produced in large quantities, a positional relationship or aconfiguration relationship between the heat transfer surface exposingportion 436 of each circuit package 400 and the bypass passage can beregularly obtained with remarkably high accuracy. Since the bypasspassage trench where the heat transfer surface exposing portion 436 ofthe circuit package 400 is fixed, for example, the bypass passage trenchon frontside 332 and the bypass passage trench on backside 334 can beformed with remarkably high accuracy, a work of forming the bypasspassage in this bypass passage trench is a work for covering both sidesof the housing 302 using the front or rear cover 303 or 304. This workis very simple and is a work process having a few factors of degradingthe measurement accuracy. In addition, the front or rear cover 303 or304 is produced through a resin molding process having high formationaccuracy. Therefore, it is possible to form the bypass passage providedin a specific relationship with the heat transfer surface exposingportion 436 of the circuit package 400 with high accuracy. In thismanner, it is possible to obtain high productivity in addition toimprovement of measurement accuracy.

In comparison, in the related art, the thermal flow meter was producedby fabricating the bypass passage and then bonding the measuring portionto the bypass passage using an adhesive. Such a method of using anadhesive is disadvantageous because a thickness of the adhesive isirregular, and a position or angle of the adhesive is different in eachproduct. For this reason, there was a limitation in improvement of themeasurement accuracy. If this work is performed in mass production, itis further difficult to improve the measurement accuracy.

In the embodiment according to the invention, first, the circuit package400 having the air flow sensing portion 602 is produced through a firstresin molding process, and the circuit package 400 is then fixed throughresin molding while the bypass passage trench for forming the bypasspassage through resin molding is formed through a second resin moldingprocess. As a result, it is possible to form the shape of the bypasspassage trench and fix the air flow sensing portion 602 to the bypasspassage trench with significantly high accuracy.

A portion relating to the measurement of the flow rate, such as the heattransfer surface exposing portion 436 of the air flow sensing portion602 or the measurement surface 430 installed in the heat transfersurface exposing portion 436, is formed on the surface of the circuitpackage 400. Then, the measurement surface 430 and the heat transfersurface exposing portion 436 are exposed from the resin used to form thehousing 302. That is, the heat transfer surface exposing portion 436 andthe measurement surface 430 around the heat transfer surface exposingportion 436 are not covered by the resin used to form the housing 302.The measurement surface 430 formed through the resin molding of thecircuit package 400, the heat transfer surface exposing portion 436, orthe temperature detecting portion 452 is directly used even after theresin molding of the housing 302 to measure a flow rate of the thermalflow meter 300 or a temperature. As a result, the measurement accuracyis improved.

In the embodiment according to the invention, the circuit package 400 isintegratedly formed with the housing 302 to fix the circuit package 400to the housing 302 having the bypass passage. Therefore, it is possibleto fix the circuit package 400 to the housing 302 with a small fixationarea. That is, it is possible to increase the surface area of thecircuit package 400 that does not make contact with the housing 302. Thesurface of the circuit package 400 that does not make contact with thehousing 302 is exposed to, for example, a gap. The heat of the intakepipe is transferred to the housing 302 and is then transferred from thehousing 302 to the circuit package 400. Even if the contact area betweenthe housing 302 and the circuit package 400 is reduced instead ofenveloping the entire surface or most of the surface of the circuitpackage 400 with the housing 302, it is possible to maintain highreliability with high accuracy and fix the circuit package 400 to thehousing 302. For this reason, it is possible to suppress heat transferfrom the housing 302 to the circuit package 400 and suppress a decreaseof the measurement accuracy.

In the embodiment illustrated in FIG. 5(A), 5(B), 6(A), or 6(B), thearea A of the exposed surface of the circuit package 400 can be set tobe equal to or larger than the area B covered by a molding material usedto form the housing 302. In the embodiment, the area A is larger thanthe area B. As a result, it is possible to suppress heat transfer fromthe housing 302 to the circuit package 400. In addition, it is possibleto reduce a stress generated by a difference between a thermal expansioncoefficient of the thermosetting resin used to form the circuit package400 and a thermal expansion coefficient of the thermoplastic resin usedto form the housing 302.

4.4 Fixation of Circuit Package 400 through Second Resin Molding Processand Effects Thereof

In FIGS. 11(A), 11(B), and 11(C), the hatching portion indicates afixation surface 432 and a fixation surface 434 for covering the circuitpackage 400 using the thermoplastic resin used in the second resinmolding process to fix the circuit package 400 to the housing 302 in thesecond resin molding process. As described above in relation to FIG.5(A), 5(B), 6(A), or 6(B), it is important to maintain high accuracy toprovide a specific relationship between the measurement surface 430, theheat transfer surface exposing portion 436 provided in the measurementsurface 430, and the shape of the bypass passage. In the second resinmolding process, the bypass passage is formed, and the circuit package400 is fixed to the housing 302 that forms the bypass passage.Therefore, it is possible to maintain a relationship between the bypasspassage, the measurement surface 430, and the heat transfer surfaceexposing portion 436 with significantly high accuracy. That is, sincethe circuit package 400 is fixed to the housing 302 in the second resinmolding process, it is possible to position and fix the circuit package400 into the die used to form the housing 302 having the bypass passagewith high accuracy. By injecting a thermoplastic resin having a hightemperature into this die, the bypass passage is formed with highaccuracy, and the circuit package 400 is fixed with high accuracy.

In this embodiment, the entire surface of the circuit package 400 is nota fixation surface 432 covered by the resin used to form the housing302, but the front surface is exposed to the connection terminal 412side of the circuit package 400. That is, a portion not covered by theresin used to form the housing 302 is provided. In the embodimentillustrated in FIGS. 11(A) to 11(C), out of the front surface of thecircuit package 400, the area that is not enveloped by the resin used toform the housing 302 but is exposed from the resin used to form thehousing 302 is larger than the area of the fixation surface 432 and thefixation surface 434 enveloped by the resin used to form the housing302.

A thermal expansion coefficient is different between the thermosettingresin used to form the circuit package 400 and the thermoplastic resinused to form the housing 302 having the fixing portion 372. It ispreferable to prevent a stress caused by this difference of the thermalexpansion coefficient from being applied to the circuit package 400 aslong as possible. By reducing the front surface of the circuit package400 and the fixation surface 432, it is possible to reduce influencebased on the difference of the thermal expansion coefficient. Forexample, it is possible to reduce the fixation surface 432 on the frontsurface of the circuit package 400 by providing a band shape having awidth L.

It is possible to increase a mechanical strength of the protrusion 424by providing the fixation surface 432 in the base of the protrusion 424.It is possible to more robustly fix the circuit package 400 and thehousing 302 to each other by providing, on the front surface of thecircuit package 400, a band-shaped fixation surface along a flow axis ofthe measurement target gas 30 and a fixation surface across the flowaxis of the measurement target gas 30. On the fixation surface 432, aportion surrounding the circuit package 400 in a band shape having awidth L along the measurement surface 430 is the fixation surface alongthe flow axis of the measurement target gas 30 described above, and aportion that covers the base of the protrusion 424 is the fixationsurface across the flow axis of the measurement target gas 30.

In FIGS. 11(A), 11(B), and 11(C), the circuit package 400 is formedthrough the first resin molding process as described above. It is notedthat the hatching portion in the appearance of the circuit package 400indicates the fixation surface 432 and the fixation surface 434 wherethe circuit package 400 is covered by the resin used in the second resinmolding process when the housing 302 is molded through the second resinmolding process after the circuit package 400 is manufactured throughthe first resin molding process. FIG. 11(A) is a left side viewillustrating the circuit package 400, FIG. 11(B) is a front viewillustrating the circuit package 400, and the FIG. 11(C) is a rear viewillustrating the circuit package 400. The circuit package 400 isembedded with the air flow sensing portion 602 or the processing unit604 described below, and they are integrally molded using athermosetting resin. On the surface of the circuit package 400 of FIG.11(B), the measurement surface 430 serving as a plane for the flow ofthe measurement target gas 30 is molded in a shape extending in a flowdirection of the measurement target gas 30. In this embodiment, themeasurement surface 430 has a rectangular shape extending in the flowdirection of the measurement target gas 30. The measurement surface 430is formed to be thinner than other portions as illustrated in FIG.11(A), and a part thereof is provided with the heat transfer surfaceexposing portion 436. The embedded air flow sensing portion 602 performsheat transfer to the measurement target gas 30 through the heat transfersurface exposing portion 436 to measure a condition of the measurementtarget gas 30 such as a flow velocity of the measurement target gas 30and output an electric signal representing the flow rate of the mainpassage 124.

In order to measure a condition of the measurement target gas 30 withhigh accuracy using the embedded air flow sensing portion 602 (refer toFIG. 19), the gas flowing through the vicinity of the heat transfersurface exposing portion 436 preferably makes a laminar flow having alittle vortex. For this reason, it is preferable that there be no heightdifference between the flow path side surface of the heat transfersurface exposing portion 436 and the plane of the measurement surface430 that guides the gas. In this configuration, it is possible tosuppress an irregular stress or a distortion from being applied to theair flow sensing portion 602 while maintaining high flow ratemeasurement accuracy. It is noted that the aforementioned heightdifference may be provided if it does not affect the flow ratemeasurement accuracy.

On the rear surface of the measurement surface 430 of the heat transfersurface exposing portion 436, a press imprint 442 of the die thatsupports an internal substrate or plate during the resin molding of thecircuit package 400 remains as illustrated in FIG. 11(C). The heattransfer surface exposing portion 436 is used to perform heat exchangewith the measurement target gas 30. In order to accurately measure acondition of the measurement target gas 30, it is preferable toappropriately perform heat transfer between the air flow sensing portion602 and the measurement target gas 30. For this reason, it is necessaryto avoid a part of the heat transfer surface exposing portion 436 frombeing covered by the resin in the first resin molding process. Dies areinstalled in both the heat transfer surface exposing portion 436 and thebackside of measurement surface 431 as a rear surface thereof, and aninflow of the resin to the heat transfer surface exposing portion 436 isprevented using the dies. A press imprint 442 having a concave shape ismolded on the rear surface of the heat transfer surface exposing portion436. In this portion, it is preferable to arrange a device serving asthe air flow sensing portion 602 or the like in the vicinity todischarge the heat generated from the device to the outside as much aspossible. The molded concave portion is less influenced by the resin andeasily discharges heat.

The heat transfer surface exposing portion 436 is internally providedwith the semiconductor diaphragm serving as the air flow sensing portion602, and a gap is molded in the rear surface of the semiconductordiaphragm. If the gap is covered, the semiconductor diaphragm isdeformed, and the measurement accuracy is degraded due to a change ofthe pressure inside the gap caused by a change of the temperature. Forthis reason, in this embodiment, an opening 438 communicating with thegap of the rear surface of the semiconductor diaphragm is provided onthe front surface of the circuit package 400, and a link channel forlinking the gap of the rear surface of the semiconductor diaphragm andthe opening 438 is provided inside the circuit package 400. It is notedthat the opening 438 is provided in the portion not hatched in FIGS.11(A) to 11(C) in order to prevent the opening 438 from being covered bythe resin through the second resin molding process.

It is necessary to mold the opening 438 through the first resin moldingprocess while an inflow of the resin to the portion of the opening 438is suppressed by matching dies to both a portion of the opening 438 anda rear surface thereof and pressing the dies. The molding of the opening438 and the link channel that connects the gap on the rear surface ofthe semiconductor diaphragm and the opening 438 will be described below.

In the circuit package 400, the press imprint 442 remains on the rearsurface of the circuit package 400 where the heat transfer surfaceexposing portion 436 is formed. In the first resin molding process, inorder to prevent an inflow of the resin to the heat transfer surfaceexposing portion 436, a die such as an insertion die is installed in aportion of the heat transfer surface exposing portion 436, and a die isinstalled in a portion of the press imprint 442 opposite thereto, sothat an inflow of the resin to the heat transfer surface exposingportion 436 is suppressed. By molding a portion of the heat transfersurface exposing portion 436 in this manner, it is possible to measurethe flow rate of the measurement target gas 30 with significantly highaccuracy. In addition, since the resin does not remain at all or less inthe portion of the press imprint 442 through the second resin moldingprocess, a hear radiation effect is increased. In a case where a secondplate 536 is used as the lead, the neighboring circuits can beeffectively heated and radiated through the lead.

5. Mounting of Circuit Components to Circuit Package

5.1 Mounting of Frame of Circuit Package and Circuit Components

FIG. 12 illustrates a frame 512 of the circuit package 400 and amounting state of a chip as a circuit component 516 mounted on the frame512. It is noted that the dotted line 508 indicates a portion covered bythe die used to mold the circuit package 400. A lead 514 is mechanicallyconnected to the frame 512, and a plate 532 is mounted in the center ofthe frame 512. A chip-like air flow sensing portion 602 and a processingunit 604 as a larger scale integrated (LSI) circuit are mounted on theplate 532. A diaphragm 672 is provided in the air flow sensing portion602, and each terminal of the air flow sensing portion 602 describedbelow and the processing unit 604 are connected using a wire 542.Moreover, each terminal of the processing unit 604 and a correspondinglead 514 are connected using a wire 543. In addition, the lead 514positioned between a portion corresponding to the connection terminal ofthe circuit package 400 and the plate 532 is connected to the chip-likecircuit component 516 therebetween.

The air flow sensing portion 602 having the diaphragm 672 is arranged inthe most leading end side when the circuit package 400 is obtained inthis manner. The processing unit 604 is arranged in the sidecorresponding to the connection terminal for the air flow sensingportion 602 in an LSI state. In addition, a connection wire 543 isarranged in the terminal side of the processing unit 604. Bysequentially arranging the air flow sensing portion 602, the processingunit 604, the wire 543, the circuit component 516, and the connectionlead 514 in this order from the leading end side of the circuit package400 to the connection terminal, the entire circuit package 400 becomessimple and concise.

A thick lead is provided to support the plate 532, and this lead isfixed to the frame 512 using the lead 556 or 558. It is noted that alead surface having the same area as that of the plate 532 connected tothe thick lead is provided on the lower surface of the plate 532, andthe plate 532 is mounted on the lead surface. This lead surface isgrounded. As a result, it is possible to suppress noise by commonlygrounding the circuit of the air flow sensing portion 602 or theprocessing unit 604 using the lead surface, so that measurement accuracyof the measurement target gas 30 is improved. In addition, a lead 544 isprovided in the upstream side of the flow path from the plate 532, thatis, so as to protrude along an axis directed across the axis of the airflow sensing portion 602, the processing unit 604, or the circuitcomponent 516 described above. A temperature detection element 518, forexample, a chip-like thermistor is connected to this lead 544. Inaddition, a lead 548 is provided in the vicinity of the processing unit604 which is a base of the protrusion, and the leads 544 and 548 areelectrically connected using a thin connection line 546 such as an Auwire. As the leads 548 and 544 are directly connected, the heat istransferred to the temperature detection element 518 through the leads548 and 544, so that it may be difficult to accurately measure atemperature of the measurement target gas 30. For this reason, byconnecting a wire having a small cross-sectional area and a largethermal resistance, it is possible to increase a thermal resistancebetween the leads 548 and 544. As a result, it is possible to improvetemperature measurement accuracy of the measurement target gas 30 so asto prevent influence of the heat from reaching the temperature detectionelement 518.

The lead 548 is fixed to the frame 512 through the lead 552 or 554. Aconnection portion between the lead 552 or 554 and the frame 512 isfixed to the frame 512 while it is inclined against the protrudingdirection of the protruding temperature detection element 518, and thedie is also inclined in this area. As the molding resin flows along inthis inclination in the first resin molding process, the molding resinof the first resin molding process smoothly flows to the leading endportion where the temperature detection element 518 is provided, so thatreliability is improved.

In FIG. 12, an arrow 592 indicates a resin injection direction. The leadframe where a circuit component is mounted is covered by the die, and apressed fitting hole 590 for resin injection to the die is provided in acircled position, so that a thermosetting resin is injected into the diealong the direction of the arrow 592. The circuit component 516 or thetemperature detection element 518 and the lead 544 for holding thetemperature detection element 518 are provided along the direction ofthe arrow 592 from the pressed fitting hole 590. In addition, the plate532, the processing unit 604, and the air flow sensing portion 602 arearranged in a direction close to the arrow 592. In this arrangement, theresin smoothly flows in the first resin molding process. In the firstresin molding process, a thermosetting resin is used, so that it isimportant to widen the resin before solidification. For this reason,arrangement of a circuit component of the lead 514 or a wire and arelationship between the pressed fitting hole 590 and the injectiondirection become important.

5.2 Structure for Connecting Gap on Rear Surface of Diaphragm andOpening

FIG. 13 is a diagram illustrating a part of the cross section takenalong a line C-C of FIG. 12 for describing the diaphragm 672 and acommunication hole 676 that connects a gap 674 provided inside thediaphragm 672 and the hole 520.

As described below, the air flow sensing portion 602 for measuring theflow rate of the measurement target gas 30 is provided with a diaphragm672, and a gap 674 is provided on the rear surface of the diaphragm 672.Although not illustrated, the diaphragm 672 is provided with an elementfor exchanging heat with the measurement target gas 30 and measuring theflow rate thereby. If the heat is transferred to the elements formed inthe diaphragm 672 through the diaphragm 672 separately from the heatexchange with the measurement target gas 30, it is difficult toaccurately measure the flow rate. For this reason, it is necessary toincrease a thermal resistance of the diaphragm 672 and form thediaphragm 672 as thin as possible.

The diaphragm 672 is buried and fixed into the first resin of thecircuit package 400 formed through the first resin molding process, andthe surface of the diaphragm 672 is provided with the elements (notillustrated). The elements perform heat transfer with the measurementtarget gas 30 (not illustrated) through the heat transfer surface 437 onthe surface of the elements in the heat transfer surface exposingportion 436. The heat transfer surface 437 may be provided on thesurface of each element or may be provided with a thin protection filmthereon. It is preferable that heat transfer between the elements andthe measurement target gas 30 be smoothly performed, and direct heattransfer between the elements be reduced as much as possible.

A portion of the diaphragm 672 where the elements are provided isarranged in the heat transfer surface exposing portion 436 of themeasurement surface 430, and the heat transfer surface 437 is exposedfrom the resin used to form the measurement surface 430. The outercircumference of the diaphragm 672 is covered by the thermosetting resinused in the first resin molding process for forming the measurementsurface 430. If only the side face of the diaphragm 672 is covered bythe thermosetting resin, and the surface side of the outer circumferenceof the diaphragm 672 is not covered by the thermosetting resin, a stressgenerated in the resin used to form the measurement surface 430 isreceived only by the side face of the diaphragm 672, so that adistortion may generated in the diaphragm 672, and characteristics maybedeteriorated. The distortion of the diaphragm 672 is reduced by coveringthe outer circumference portion of the diaphragm 672 with thethermosetting resin as illustrated in FIG. 13. Meanwhile, if a heightdifference between the heat transfer surface 437 and the measurementsurface 430 where the measurement target gas 30 flows is large, the flowof the measurement target gas 30 is disturbed, so that measurementaccuracy is degraded. Therefore, it is preferable that a heightdifference W between the heat transfer surface 437 and the measurementsurface 430 where the measurement target gas 30 flows be small.

The diaphragm 672 is formed thin in order to suppress heat transferbetween each element, and a gap 674 is formed in the rear surface of thediaphragm 672. If this gap 674 is sealed, a pressure of the gap 674formed on the rear surface of the diaphragm 672 changes depending on atemperature change. As a pressure difference between the gap 674 and thesurface of the diaphragm 672 increases, the diaphragm 672 receives thepressure, and a distortion is generated, so that high accuracymeasurement becomes difficult. For this reason, a hole 520 connected tothe opening 438 opened to the outside is provided in the plate 532, anda communication hole 676 that connects this hole 520 and the diaphragm672 is provided. This communication hole 676 consists of, for example, apair of plates including first and second plates 534 and 536. The firstplate 534 is provided with holes 520 and 521 and a trench for formingthe communication hole 676. The communication hole 676 is formed bycovering the trench and the holes 520 and 521 with the second plate 536.Using the communication hole 676 and the hole 520, the pressures appliedto the front and rear surfaces of the diaphragm 672 becomesapproximately equal, so that the measurement accuracy is improved.

As described above, the communication hole 676 can be formed by coveringthe trench and the holes 520 and 521 with the second plate 536.Alternatively, the lead frame maybe used as second plate 536. Asdescribed in relation to FIG. 12, the diaphragm 672 and the LSI circuitserving as the processing unit 604 are provided on the plate 532. A leadframe for supporting the plate 532 where the diaphragm 672 and theprocessing unit 604 are mounted is provided thereunder. Therefore, usingthe lead frame, the structure becomes simpler. In addition, the leadframe maybe used as a ground electrode. If the lead frame serves as thesecond plate 536, and the communication hole 676 is formed by coveringthe holes 520 and 521 formed in the first plate 534 using the lead frameand covering the trench formed in the first plate 534 using the leadframe in this manner, it is possible to simplify the entire structure.In addition, it is possible to reduce influence of noise from theoutside of the diaphragm 672 and the processing unit 604 because thelead frame serves as a ground electrode.

FIG. 14 illustrates a state that the frame of FIG. 12 is molded with athermosetting resin through the first resin molding process and iscovered by the thermosetting resin. Through this molding, themeasurement surface 430 is molded on the front surface of the circuitpackage 400, and the heat transfer surface exposing portion 436 isprovided on the measurement surface 430. In addition, the gap 674 on therear surface of the diaphragm 672 arranged in the inside of the heattransfer surface exposing portion 436 is connected to the opening 438.The temperature detecting portion 452 for measuring a temperature of themeasurement target gas 30 is provided in the leading end of theprotrusion 424, and the temperature detection element 518 is embeddedinside. Inside the protrusion 424, in order to suppress heat transfer, alead for extracting the electric signal of the temperature detectionelement 518 is segmented, and a connection line 546 having a largethermal resistance is arranged. As a result, it is possible to suppressheat transfer from the base of the protrusion 424 to the temperaturedetecting portion 452 and influence from the heat.

A slope portion 594 or 596 is formed in the base of the protrusion 424.A flow of the resin in the first resin molding process becomes smooth.In addition, the measurement target gas 30 measured by the temperaturedetecting portion 452 smoothly flows from the protrusion 424 to its baseusing the slope portion 594 or 596 while the temperature detectingportion 452 is installed and operated in a vehicle, so as to cool thebase of the protrusion 424. Therefore, it is possible to reduceinfluence of the heat to the temperature detecting portion 452. Afterthe state of FIG. 14, the lead 514 is separated from each terminal so asto serve as the connection terminal 412 or the terminal 414.

In the first resin molding process, it is necessary to prevent an inflowof the resin to the heat transfer surface exposing portion 436 or theopening 438. For this reason, in the first resin molding process, aninflow of the resin is suppressed in a position of the heat transfersurface exposing portion 436 or the opening 438. For example, aninsertion die larger than the diaphragm 672 is installed, and a press isinstalled in the rear surface thereof, so that it is pressed from bothsurfaces. In FIG. 11(C), the press imprint 442 or 441 remains on therear surface corresponding to the heat transfer surface exposing portion436 or the opening 438 of FIG. 14 or the heat transfer surface exposingportion 436 or the opening 438 of FIG. 11(B).

In the surface of the circuit package 400 where the heat transfersurface exposing portion 436 is formed. In the first resin moldingprocess, in order to prevent an inflow of the resin to the heat transfersurface exposing portion 436, a die such as an insertion die isinstalled in a portion of the heat transfer surface exposing portion436, and a die is installed in a portion of the press imprint 442opposite thereto, so that an inflow of the resin to the heat transfersurface exposing portion 436 is suppressed. By forming a portion of theheat transfer surface exposing portion 436 in this manner, it ispossible to measure the flow rate of the measurement target gas 30 withsignificantly high accuracy. In addition, since the resin does notremain at all or less in the portion of the press imprint 442 throughthe second resin molding process, a hear radiation effect is increased.In a case where a second plate 536 is used as the lead, the neighboringcircuits can be effectively heated and radiated through the lead.

In FIG. 14, a cutout surface of the lead separated from the frame 512 isexposed from the resin surface, so that moisture or the like may intrudeinto the inside on the cutout surface of the lead during the use. It isimportant to prevent such a problem from the viewpoint of durability orreliability. For example, a portion of the fixation surface 434 of FIG.14 is covered by the resin through the second resin molding process, andthe cutout surface is exposed. In addition, the lead cutout portion ofthe slope portion 594 or 596 is covered by the resin through the secondresin molding process, and the cutout surface between the lead 552 or554 and the frame 512 illustrated in FIG. 12 is covered by the resin. Asa result, it is possible to prevent erosion of the lead 552 or 554 orintrusion of water from the cutout portion. The cutout portion of thelead 552 or 554 adjoins an important lead portion that transmits theelectric signal of the temperature detecting portion 452. Therefore, itis preferable that the cutout portion be covered in the second resinmolding process.

5.3 Another Embodiment of Circuit Package 400

FIGS. 15(A) and 15(B) illustrate another embodiment of the circuitpackage 400. Like reference numerals denote like elements as in otherdrawings. In the embodiment described above in relation to FIGS. 11(A)to 11(C), the connection terminal 412 and the terminal 414 of thecircuit package 400 are provided in the same side of the circuit package400. In comparison, in the embodiment of FIGS. 15(A) and 15(B), theconnection terminal 412 and the terminal 414 are provided in differentsides. The terminal 414 is a terminal not connected to the connectionterminal connected to the outside in the thermal flow meter 300. If theconnection terminal 412 connected to the outside in the thermal flowmeter 300 and the terminal 414 not connected to the outside are providedin different directions in this manner, it is possible to widen adistance between the connection terminal 412 and the terminal andimprove workability. In addition, if the terminal 414 extends to adirection different from that of the connection terminal 412, it ispossible to prevent the lead inside the frame 512 from beingconcentrated on apart and facilitate arrangement of the lead inside theframe 512. In particular, a chip capacitor as the circuit component 516is connected to a portion of the lead corresponding to the connectionterminal 412. A slightly large space is necessary to provide such acircuit component 516. In the embodiment of FIGS. 15(A) and 15(B), it ispossible to easily obtain a space for the lead corresponding to theconnection terminal 412.

Similarly to the circuit package 400 illustrated in FIG. 11, the circuitpackage 400 illustrated in FIG. 15 is provided with a slope portion 462and a slope portion 464 having a smoothly-changing thickness. The slopeportions are molded in the neck portion of the protrusion 424 protrudingfrom a circuit package body 422. The same effects as described withreference to FIG. 11 are obtained. In other words, as illustrated inFIG. 15, the protrusion 424 protrudes in a shape extending to theupstream direction of the measurement target gas 30 from the sidesurface of the circuit package body 422. The temperature detectingportion 452 is provided in the leading end portion of the protrusion424, and the temperature detection element 518 is buried in the insideof the temperature detecting portion 452. The slope portions 462 and 464are provided in a portion connecting the protrusion 424 and the circuitpackage body 422. The protrusion 424 is formed such that the basethereof becomes thick by the slope portion 462 or the slope portion 464,and the neck portion of the protrusion 424 is formed gradually thin asit goes to the leading end direction.

With such a shape, in a case where the circuit package 400 is moldedthrough the resin molding, it is possible to use a method of attaching asheet inside the die for the purpose of protection of the element. Inthis case, the sheet and the inner surface of the die abut securely, sothat the reliability is improved. In addition, the mechanical strengthof the protrusion 424 is weak, so that it may be easily folded. Theprotrusion 424 is made thick in its base portion, and has the shapebeing gradually thin as it goes to the leading end direction, so thatthe stress concentration on the base can be alleviated and themechanical strength becomes excellent. In addition, in a case where theprotrusion 424 is formed through the resin molding, the protrusion iseasily bent under the influence of a volume change when the resin issolidified. Such an influence can be reduced. In order to detect thetemperature of the measurement target gas 30 as accurate as possible, itis preferable that the protrusion be formed long. The heat transfer fromthe circuit package body 422 onto the temperature detection element 518provided in the temperature detecting portion 452 becomes easily reducedby forming the protrusion 424 long.

As illustrated in FIGS. 11(B) and 11(C), the base of the protrusion 424is formed thick and the base of the protrusion 424 is surrounded by thehousing 302, and thus the circuit package 400 is fixed to the housing302. In this way, since the base of the protrusion 424 is covered withthe resin of the housing 302, it is possible to prevent the protrusion424 from taking damage due to the mechanical impact. In addition,various effects described with reference to FIG. 11 are achieved.

Descriptions for the opening 438, the heat transfer surface exposingportion 436, the measurement surface 430, the press imprint 441, and thepress imprint 442 in FIGS. 15(A) and 15(B) are similar to thosedescribed above, and they have the same functional effects. Detaileddescriptions will not be repeated for simplicity purposes.

6. Process of Producing Thermal Flow Meter 300

6.1 Process of Producing Circuit Package 400

FIG. 16 illustrates a process of producing the circuit package 400 in aprocess of producing the thermal flow meter 300. FIG. 17 illustrates aprocess of producing a thermal flow meter, and FIG. 18 illustrates aprocess of producing the thermal flow meter according to anotherembodiment. In FIG. 16, step 1 shows a process of producing a frame ofFIG. 12. This frame is formed, for example, through press machining. Instep 2, the plate 532 is first mounted on the frame obtained through thestep 1, and the air flow sensing portion 602 or the processing unit 604is further mounted on the plate 532. Then, the temperature detectionelement 518 and the circuit component such as a chip capacitor aremounted. In step 2, electric wiring is performed between circuitcomponents, between the circuit component and the lead, and between theleads. In step 2, the leads 544 and 548 are connected using a connectionline 546 for increasing a thermal resistance. In step 2, the circuitcomponent illustrated in FIG. 12 is mounted on the frame 512, and theelectric wiring is further performed, so that an electric circuit isformed.

Then, in step 3, through the first resin molding process, molding usinga thermosetting resin is performed. The molded circuit package 400 isillustrated in FIG. 14. In addition, in step 3, each of the connectedleads is separated from the frame 512, and the leads are separated fromeach other, so that the circuit package 400 of FIGS. 11(A) to 11(C) orFIGS. 15(A) and 15(B) is obtained. In this circuit package 400, asillustrated in FIGS. 11(A) to 11(C) or FIGS. 15(A) and 15(B), themeasurement surface 430 or the heat transfer surface exposing portion436 is formed.

In step 4, a visual inspection or an operational inspection is performedfor the obtained circuit package 400. In the first resin molding processof step 3, a transfer molding is performed. The electric circuitobtained in step 2 is fixed to the inside of the die, and a hightemperature resin is injected into the die with a high pressure.Therefore, it is preferable to inspect whether or not there is anabnormality in the electric component or the electric wiring. For thisinspection, the terminal 414 is used in addition to the connectionterminal 412 of FIGS. 11(A) to 11(C) or FIGS. 15(A) and 15(B). It isnoted that, because the terminal 414 is not used thereafter, it may becut out from the base after this inspection. For example, referring toFIGS. 15(A) and 15(B), the terminal 414 is cut out from the base afterthe use.

6.2 Process of Producing Thermal Flow Meter 300 and Calibration ofMeasurement Characteristic

In FIG. 17, the circuit package 400 already produced according to FIG.16 and the external terminal 306 already produced according to a method(not illustrated) are used. In step 5, the housing 302 is formed throughthe second resin molding process. The housing 302 is formed togetherwith the resin bypass passage trench, the flange 312, and the externalconnector 305. The hatching portion of the circuit package 400illustrated in FIG. 11 is covered with the resin through the secondresin molding process. The circuit package 400 is fixed to the housing302. By combining the production (step 3) of the circuit package 400through the first resin molding process and the molding of the housing302 of the thermal flow meter 300 through the second resin moldingprocess, the flow rate detection accuracy is remarkably improved. Instep 6, each inner socket of external terminal 361 illustrated in FIG.10 is separated. In step 7, the connection terminal 412 and the innersocket of external terminal 361 are connected.

The housing 302 is obtained in step 7. Then, in step 8, the front cover303 and the rear cover 304 are installed in the housing 302, so that theinside of the housing 302 is sealed with the front and rear covers 303and 304, and the bypass passage through which the measurement target gas30 flows is obtained. In this way, the thermal flow meter 300 iscompleted. In addition, an orifice structure described in relation toFIG. 7 is formed by the protrusion 356 provided in the front cover 303or the rear cover 304. It is noted that the front cover 303 is formedthrough the molding of step 10, and the rear cover 304 is formed throughthe molding of step 11. In addition, the front and rear covers 303 and304 are molded through separate processes using different dies.

In step 9, a characteristic test is performed by guiding the gas to thebypass passage in practice. Since a relationship between the bypasspassage and the air flow sensing portion is maintained with highaccuracy as described above, significantly high measurement accuracy isobtained by performing a characteristic calibration through acharacteristic test. In addition, since the molding is performed with apositioning or configuration relationship between the bypass passage andthe air flow sensing portion is determined through the first resinmolding process and the second resin molding process, the characteristicdoes not change much even in a long time use, and high reliability isobtained in addition to the high accuracy.

6.3 Another Embodiment of Process of Producing Thermal Flow Meter 300

In FIG. 18, the circuit package 400 already produced according to FIG.16 and the external terminal 306 already produced according to a method(not illustrated) are used. In step 12 before the second resin moldingprocess, the connection terminal 412 of the circuit package 400 and theinner socket of external terminals 361 are connected. In this case or inthe process prior to step 12, each inner socket of external terminal 361illustrated in FIG. 10 is separated. In step 13, the housing 302 isformed through the second resin molding process. The housing 302 isformed together with the resin bypass passage trench, the flange 312,and the external connector 305. The hatching portion of the circuitpackage 400 illustrated in FIG. 11 is covered with the resin through thesecond resin molding process. The circuit package 400 is fixed to thehousing 302. By combining the production (step 3) of the circuit package400 through the first resin molding process and the molding of thehousing 302 of the thermal flow meter 300 through the second resinmolding process, the flow rate detection accuracy is remarkablyimproved.

The housing 302 is obtained in step 13. Then, in step 8, the front andrear covers 303 and 304 are installed in the housing 302, so that theinside of the housing 302 is sealed with the front and rear covers 303and 304, and the bypass passage for flowing the measurement target gas30 is obtained. In addition, an orifice structure described in relationto FIGS. 7(A), 7(B) is formed by the protrusion 356 provided in thefront or rear cover 303 or 304. It is noted that the front cover 303 isformed through the molding of step 10, and the rear cover 304 is formedthrough the molding of step 11. In addition, the front and rear covers303 and 304 are formed through separate processes using different dies.

In step 9, a characteristic test is performed by guiding the air to thebypass passage in practice. Since a relationship between the bypasspassage and the air flow sensing portion is maintained with highaccuracy as described above, significantly high measurement accuracy isobtained by performing a characteristic calibration through acharacteristic test. In addition, since the molding is performed with apositioning or configuration relationship between the bypass passage andthe air flow sensing portion is determined through the first resinmolding process and the second resin molding process, the characteristicdoes not change much even in a long time use, and high reliability isobtained in addition to the high accuracy.

7. Circuit Configuration of Thermal Flow Meter 300

7.1 Entire Circuit Configuration of Thermal Flow Meter 300

FIG. 19 is a circuit diagram illustrating the flow rate detectioncircuit 601 of the thermal flow meter 300. It is noted that themeasurement circuit relating to the temperature detecting portion 452described in the aforementioned embodiment is also provided in thethermal flow meter 300, but is not illustrated intentionally in FIG. 19.The flow rate detection circuit 601 of the thermal flow meter 300includes the air flow sensing portion 602 having the heat generator 608and the processing unit 604. The processing unit 604 control a heatamount of the heat generator 608 of the air flow sensing portion 602 andoutputs a signal representing the flow rate through the terminal 662based on the output of the air flow sensing portion 602. For thisprocessing, the processing unit 604 includes a central processing unit(hereinafter, referred to as “CPU”) 612, an input circuit 614, an outputcircuit 616, a memory 618 for storing data representing a relationshipbetween the calibration value or the measurement value and the flowrate, and a power circuit 622 for supplying a certain voltage to eachnecessary circuit. The power circuit 622 is supplied with DC power froman external power supply such as a vehicle-mount battery through aterminal 664 and a ground terminal (not illustrated).

The air flow sensing portion 602 is provided with a heat generator 608for heating the measurement target gas 30. A voltage V1 is supplied fromthe power circuit 622 to a collector of a transistor 606 included in acurrent supply circuit of the heat generator 608, and a control signalis applied from the CPU 612 to a base of the transistor 606 through theoutput circuit 616. Based on this control signal, a current is suppliedfrom the transistor 606 to the heat generator 608 through the terminal624. The current amount supplied to the heat generator 608 is controlledby a control signal applied from the CPU 612 to the transistor 606 ofthe current supply circuit of the heat generator 608 through the outputcircuit 616. The processing unit 604 controls the heat amount of theheat generator 608 such that a temperature of the measurement target gas30 increases by a predetermined temperature, for example, 100° C. froman initial temperature by heating using the heat generator 608.

The air flow sensing portion 602 includes a heating control bridge 640for controlling a heat amount of the heat generator 608 and a bridgecircuit of air flow sensing 650 for measuring a flow rate. Apredetermined voltage V3 is supplied to one end of the heating controlbridge 640 from the power circuit 622 through the terminal 626, and theother end of the heating control bridge 640 is connected to the groundterminal 630. In addition, a predetermined voltage V2 is applied to oneend of the bridge circuit of air flow sensing 650 from the power circuit622 through the terminal 625, and the other end of the bridge circuit ofair flow sensing 650 is connected to the ground terminal 630.

The heating control bridge 640 has a resistor 642 which is a resistancetemperature detector having a resistance value changing depending on thetemperature of the heated measurement target gas 30, and the resistors642, 644, 646, and 648 constitute a bridge circuit. A potentialdifference between a node A between the resistors 642 and 646 and a nodeB between the resistors 644 and 648 is input to the input circuit 614through the terminals 627 and 628, and the CPU 612 controls the currentsupplied from the transistor 606 to control the heat amount of the heatgenerator 608 such that the potential difference between the nodes A andB is set to a predetermined value, for example, zero voltage in thisembodiment. The flow rate detection circuit 601 illustrated in FIG. 19heats the measurement target gas 30 using the heat generator 608 suchthat a temperature increases by a predetermined temperature, forexample, 100° C. from an initial temperature of the measurement targetgas 30 at all times. In order to perform this heating control with highaccuracy, resistance values of each resistor of the heating controlbridge 640 are set such that the potential difference between the nodesA and B becomes zero when the temperature of the measurement target gas30 heated by the heat generator 608 increases by a predeterminedtemperature, for example, 100° C. from an initial temperature at alltimes. Therefore, in the flow rate detection circuit 601 of FIG. 19, theCPU 612 controls the electric current supplied to the heat generator 608such that the potential difference between the nodes A and B becomeszero.

The bridge circuit of air flow sensing 650 includes four resistancetemperature detectors of resistors 652, 654, 656, and 658. The fourresistance temperature detectors are arranged along the flow of themeasurement target gas 30 such that the resistors 652 and 654 arearranged in the upstream side in the flow path of the measurement targetgas 30 with respect to the heat generator 608, and the resistors 656 and658 are arranged in the downstream side in the flow path of themeasurement target gas 30 with respect to the heat generator 608. Inaddition, in order to increase the measurement accuracy, the resistors652 and 654 are arranged such that distances to the heat generator 608are approximately equal, and the resistors 656 and 658 are arranged suchthat distances to the heat generator 608 are approximately equal.

A potential difference between a node C between the resistors 652 and656 and a node D between the resistors 654 and 658 is input to the inputcircuit 614 through the terminals 631 and 632. In order to increase themeasurement accuracy, each resistance of the bridge circuit of air flowsensing 650 is set, for example, such that a positional differencebetween the nodes C and D is set to zero while the flow of themeasurement target gas 30 is set to zero. Therefore, while the potentialdifference between the nodes C and D is set to, for example, zero, theCPU 612 outputs, from the terminal 662, an electric signal indicatingthat the flow rate of the main passage 124 is zero based on themeasurement result that the flow rate of the measurement target gas 30is zero.

When the measurement target gas 30 flows along the arrow direction inFIG. 19, the resistor 652 or 654 arranged in the upstream side is cooledby the measurement target gas 30, and the resistors 656 and 658 arrangedin the downstream side of the measurement target gas 30 are heated bythe measurement target gas 30 heated by the heat generator 608, so thatthe temperature of the resistors 656 and 658 increases. For this reason,a potential difference is generated between the nodes C and D of thebridge circuit of air flow sensing 650, and this potential difference isinput to the input circuit 614 through the terminals 631 and 632. TheCPU 612 searches data indicating a relationship between the flow rate ofthe main passage 124 and the aforementioned potential difference storedin the memory 618 based on the potential difference between the nodes Cand D of the bridge circuit of air flow sensing 650 to obtain the flowrate of the main passage 124. An electric signal indicating the flowrate of the main passage 124 obtained in this manner is output throughthe terminal 662. It is noted that, although the terminals 664 and 662illustrated in FIG. 19 are denoted by new reference numerals, they areincluded in the connection terminal 412 of FIG. 5(A), 5(B), 6(A), 6(B),or 10 described above.

The memory 618 stores the data indicating a relationship between thepotential difference between the nodes C and D and the flow rate of themain passage 124 and calibration data for reducing a measurement errorsuch as a variation, obtained based on the actual measurement value ofthe gas after production of the circuit package 400. It is noted thatthe actual measurement value of the gas after production of the circuitpackage 400 and the calibration value based thereon are stored in thememory 618 using the external terminal 306 or the calibration terminal307 illustrated in FIGS. 4(A) and 4(B). In this embodiment, the circuitpackage 400 is produced while an arrangement relationship between thebypass passage for flowing the measurement target gas 30 and themeasurement surface 430 or an arrangement relationship between thebypass passage for flowing the measurement target gas 30 and the heattransfer surface exposing portion 436 is maintained with high accuracyand a little variation. Therefore, it is possible to obtain ameasurement result with remarkably high accuracy through calibrationusing the calibration value.

7.2 Configuration of Flow Rate Detection Circuit 601

FIG. 20 is a circuit configuration diagram illustrating a circuitarrangement of the flow rate detection circuit 601 of FIG. 19 describedabove. The flow rate detection circuit 601 is manufactured from asemiconductor chip having a rectangular shape. The measurement targetgas 30 flows along the arrow direction from the left side to the rightside of the flow rate detection circuit 601 illustrated in FIG. 20.

A diaphragm 672 having a rectangular shape is formed in the air flowsensing portion 602. The diaphragm 672 is provided with a thin area 603(indicated by the dotted line) with the thin semiconductor chip. The gapis formed in the rear surface side of the thin area 603 and communicateswith the opening 438 illustrated in FIGS. 11(A) to 11(C) or FIGS. 5(A)and 5(B), so that the gas pressure inside the gap depends on thepressure of the gas guided from the opening 438.

By reducing the thickness of the thin area 603 of the diaphragm 672, thethermal conductivity is lowered, and heat transfer to the resistors 652,654, 658, and 656 provided in the thin area 603 through the diaphragm672 is suppressed, so that the temperatures of the resistors areapproximately set through heat transfer with the measurement target gas30.

The heat generator 608 is provided in the center of the thin area 603 ofthe diaphragm 672, and the resistor 642 of the heating control bridge640 is provided around the heat generator 608. In addition, theresistors 644, 646, and 648 of the heating control bridge 640 areprovided in the outer side of the thin area 603. The resistors 642, 644,646, and 648 formed in this manner constitute the heating control bridge640.

In addition, the resistors 652 and 654 as upstream resistancetemperature detectors and the resistors 656 and 658 as downstreamresistance temperature detectors are arranged to interpose the heatgenerator 608. The resistors 652 and 654 as upstream resistancetemperature detectors are arranged in the upstream side in the arrowdirection where the measurement target gas 30 flows with respect to theheat generator 608. The resistors 656 and 658 as downstream resistancetemperature detectors are arranged in the downstream side in the arrowdirection where the measurement target gas 30 flows with respect to theheat generator 608. In this manner, the bridge circuit of air flowsensing 650 is formed by the resistors 652, 654, 656, and 658 arrangedin the thin area 603.

Both ends of the heat generator 608 are connected to each of theterminals 624 and 629 illustrated in the lower half of FIG. 20. Here, asillustrated in FIG. 19, the current supplied from the transistor 606 tothe heat generator 608 is applied to the terminal 624, and the terminal629 is grounded.

The resistors 642, 644, 646, and 648 of the heating control bridge 640are connected to each other and are connected to the terminals 626 and630. As illustrated in FIG. 19, the terminal 626 is supplied with apredetermined voltage V3 from the power circuit 622, and the terminal630 is grounded. In addition, the node between the resistors 642 and 646and the node between the resistors 646 and 648 are connected to theterminals 627 and 628, respectively. As illustrated in FIG. 20, theterminal 627 outputs an electric potential of the node A between theresistors 642 and 646, and the terminal 627 outputs an electricpotential of the node B between the resistors 644 and 648. Asillustrated in FIG. 19, the terminal 625 is supplied with apredetermined voltage V2 from the power circuit 622, and the terminal630 is grounded as a ground terminal. In addition, a node between theresistors 654 and 658 is connected to the terminal 631, and the terminal631 outputs an electric potential of the node B of FIG. 19. The nodebetween the resistors 652 and 656 is connected to the terminal 632, andthe terminal 632 outputs an electric potential of the node C illustratedin FIG. 19.

As illustrated in FIG. 20, since the resistor 642 of the heating controlbridge 640 is formed in the vicinity of the heat generator 608, it ispossible to measure the temperature of the gas heated by the heat fromthe heat generator 608 with high accuracy. Meanwhile, since theresistors 644, 646, and 648 of the heating control bridge 640 arearranged distant from the heat generator 608, they are not easilyinfluenced by the heat generated from the heat generator 608. Theresistor 642 is configured to respond sensitively to the temperature ofthe gas heated by the heat generator 608, and the resistors 644, 646,and 648 are configured not to be influenced by the heat generator 608.For this reason, the detection accuracy of the measurement target gas 30using the heating control bridge 640 is high, and the control forheating the measurement target gas 30 by only a predeterminedtemperature from its initial temperature can be performed with highaccuracy.

In this embodiment, a gap is formed in the rear surface side of thediaphragm 672 and communicates with the opening 438 illustrated in FIGS.11(A) to 11(C) or 5(A) and 5(B), so that a difference between thepressure of the gap in the backside of the diaphragm 672 and thepressure in the front side of the diaphragm 672 does not increase. It ispossible to suppress a distortion of the diaphragm 672 caused by thispressure difference. This contributes to improvement of the flow ratemeasurement accuracy.

As described above, the heat conduction through the diaphragm 672 issuppressed as small as possible by molding the thin area 603 andreducing the thickness of the thin area 603 in the diaphragm 672.Therefore, while influence of the heat conduction through the diaphragm672 is suppressed, the bridge circuit of air flow sensing 650 or theheating control bridge 640 more strongly tends to operate depending onthe temperature of the measurement target gas 30, so that themeasurement operation is improved. For this reason, high measurementaccuracy is obtained.

8. Measuring of Gas Temperature in Thermal Flow Meter 300

8.1 Structure of Temperature Detecting Portion 452 in Thermal Flow Meter300

In FIGS. 2(A), 2(B), 3(A), and 3(B), the inlet port 343 is positioned inthe flange 312 side from the bypass passage provided in the leading endside of the measuring portion 310 and is opened toward an upstream sideof the flow of the measurement target gas 30. Inside the inlet port 343,a temperature detecting portion 452 is arranged to measure a temperatureof the measurement target gas 30. In the center of the measuring portion310 where the inlet port 343 is provided, an upstream-side outer wall ofthe measuring portion 310 included in the housing 302 is hollowed towardthe downstream side (that is, the inside of the housing 302), and thetemperature detecting portion 452 is formed to protrude toward theupstream side from the upstream-side outer wall having the hollow shapeto the outside from the housing 302. In addition, front and rear covers303 and 304 are provided in both sides of the outer wall having a hollowshape, and the upstream side ends of the front and rear covers 303 and304 are formed to protrude toward the upstream side from the outer wallhaving the hollow shape. For this reason, the inlet port 343 forreceiving the measurement target gas 30 is molded by the outer wallhaving the hollow shape and the front and rear covers 303 and 304 in itsboth sides. The measurement target gas 30 received from the inlet port343 makes contact with the temperature detecting portion 452 providedinside the inlet port 343 to measure the temperature of the temperaturedetecting portion 452. Furthermore, the measurement target gas 30 flowsalong a portion that supports the temperature detecting portion 452protruding from the outer wall of the housing 302 having a hollow shapeto the upstream side, and is discharged to the main passage 124 from afront side outlet port 344 and a backside outlet port 345 provided inthe front and rear covers 303 and 304.

8.2 Functional Effects of Temperature Detecting Portion 452

As illustrated in FIGS. 2 and 3, the temperature detecting portion 452protrudes to the outside from the housing 302 and makes a direct contactwith the measurement target gas 30, so that the detection accuracy isimproved. In addition, a temperature of the gas flowing to the inletport 343 from the upstream side of the direction along the flow of themeasurement target gas 30 is measured by the temperature detectingportion 452. Furthermore, the gas flows toward a neck portion of thetemperature detecting portion 452 for supporting the temperaturedetecting portion 452, so that it lowers the temperature of the portionfor supporting the temperature detecting portion 452 to the vicinity ofthe temperature of the measurement target gas 30. The temperature of theintake pipe serving as a main passage 124 typically increases, and theheat is transferred to the portion for supporting the temperaturedetecting portion 452 through the upstream-side outer wall inside themeasuring portion 310 from the flange 312 or the thermal insulation 315,so that the temperature measurement accuracy may be influenced. Asdescribed above, the support portion is cooled as the measurement targetgas 30 is measured by the temperature detecting portion 452 and thenflows along the support portion of the temperature detecting portion452. Therefore, it is possible to suppress the heat from beingtransferred to the portion for supporting the temperature detectingportion 452 through the upstream-side outer wall inside the measuringportion 310 from the flange 312 or the thermal insulation 315.

In particular, in the support portion of the temperature detectingportion 452, the upstream-side outer wall inside the measuring portion310 has a shape concave to the downstream side. Therefore, it ispossible to increase a distance between the upstream-side outer wallinside the measuring portion 310 and the temperature detecting portion452. While the heat conduction length increases, a distance of thecooling portion using the measurement target gas 30 increases.Therefore, it is also possible to reduce influence of the heat from theflange 312 or the thermal insulation 315. Accordingly, the measurementaccuracy is improved.

Since the upstream-side outer wall has a shape concave to the downstreamside, that is, the inside of the housing 302, it can be fixed by theupstream-side outer wall 335 of the housing 302 and the fixation of thecircuit package 400 becomes easy. In addition, it is also effective tothe strength of the protrusion 424 (refer to FIG. 11) having thetemperature detecting portion 452.

As illustrated above with reference to FIGS. 2 and 3, the inlet port 343is provided on the upstream side of the measurement target gas 30 in thecase 301. The measurement target gas 30 guided from the inlet port 343passes through the vicinity of the temperature detecting portion 452 andis guided to the main passage 124 from the front side outlet port 344and the backside outlet port 345. The temperature detecting portion 452measures the temperature of the measurement target gas 30. The electricsignal representing the temperature measured by the external terminal306 of the external connector 305 is output. The case 301 of the thermalflow meter 300 includes the front cover 303, the rear cover 304, and thehousing 302. The housing 302 includes the hollow for molding the inletport 343. The hollow is formed by the outer wall hollow portion 366(refer to FIGS. 5 and 6). In addition, the front side outlet port 344 orthe backside outlet port 345 is molded by the hole provided in the frontcover 303 or the rear cover 304. As described above, the temperaturedetecting portion 452 is provided with the leading end portion of theprotrusion 424, and has a weak mechanical strength. The front cover 303or the rear cover 304 serves to protect the protrusion 424 against themechanical impact.

In addition, the front protection portion 322 or the rear protectionportion 325 is molded in the front or rear cover 303 or 304 illustratedin FIGS. 8(A) to 8(C) or FIGS. 9(A) to 9(C). As illustrated in FIG.2(A), 2(B), 3(A), or 3(B), the front protection portion 322 provided inthe front cover 303 is arranged on the front side surface of the inletport 343, and the rear protection portion 325 provided in the rear cover304 is arranged in the backside surface of the inlet port 343. Thetemperature detecting portion 452 arranged inside the inlet port 343 isprotected by the front protection portion 322 and the rear protectionportion 325, so that it is possible to prevent a mechanical damage ofthe temperature detecting portion 452 caused when the temperaturedetecting portion 452 collides with something during production orloading on a vehicle.

8.3 Formation of Temperature Detecting Portion 452 and Protrusion 424and Effects Thereof

The circuit package 400 includes the circuit package body 422 and theprotrusion 424 embedding the air flow sensing portion 602 and theprocessing unit 604 for measuring the flow rate. As illustrated in thedrawing, the protrusion 424 protrudes in a shape extending to theupstream direction of the measurement target gas 30 from the sidesurface of the circuit package body 422. The temperature detectingportion 452 is provided in the leading end portion of the protrusion424, and the temperature detection element 518 is buried in the insideof the temperature detecting portion 452. The slope portions 462 and 464are provided in a portion connecting the protrusion 424 and the circuitpackage body 422. The protrusion 424 is formed such that the basethereof becomes thick by the slope portion 462 or the slope portion 464,and the neck portion of the protrusion 424 is formed gradually thin asit goes to the leading end direction.

In addition, in a case where the protrusion 424 is formed through theresin molding, the protrusion is easily bent under the influence of avolume change when the resin is solidified. By making the base thick,such a problem can also be reduced. Furthermore, in order to detect thetemperature of the measurement target gas 30 as accurate as possible, itis preferable that the protrusion be formed long. With the thick base,the protrusion 424 can be formed long, and the detection accuracy of thetemperature detection element 518 provided in the temperature detectingportion 452 is improved.

As illustrated in FIGS. 11(B) and 11(C), the base of the protrusion 424is formed thick and the base of the protrusion 424 is surrounded by thehousing 302, and thus the circuit package 400 is fixed to the housing302. In this way, since the base of the protrusion 424 is covered withthe resin of the housing 302, it is possible to prevent the protrusion424 from taking damage due to the mechanical impact.

In order to detect the temperature of the measurement target gas 30 withhigh accuracy, it is preferably controlled the heat transfer from themain passage 124 installed in the thermal flow meter 300 through thehousing 302 or the circuit package 400. The protrusion 424 supportingthe temperature detecting portion 452 has the leading end portionthinner than the base thereof. The temperature detecting portion 452 isprovided in the leading end portion. With such a structure, theinfluence of the heat from the neck portion of the protrusion 424 to thetemperature detecting portion 452 is reduced.

In addition, after the temperature of the measurement target gas 30 isdetected by the temperature detecting portion 452, the measurementtarget gas 30 flows along the protrusion 424, and the temperature of theprotrusion 424 approaches the temperature of the measurement target gas30. Therefore, the influence of the temperature of the neck portion ofthe protrusion 424 on the temperature detecting portion 452 issuppressed. Specifically, in the embodiment, the vicinity of theprotrusion 424 provided with the temperature detecting portion 452 isformed thin and becomes thicker as it goes to the base of the protrusion424. For this reason, the measurement target gas 30 flows along thestructure of the protrusion 424, and thus the protrusion 424 isefficiently cooled.

The hatching portion of the neck portion of the protrusion 424 is afixation surface 432 covered by the resin used to mold the housing 302in the second resin molding process. A hollow is provided in thehatching portion of the neck portion of the protrusion 424. This showsthat a portion of the hollow shape not covered by the resin of thehousing 302 is provided. If such a portion having a hollow shape notcovered by the resin of the housing 302 in the neck portion of theprotrusion 424 is provided in this manner, it is possible to furthereasily cool the protrusion 424 using the measurement target gas 30.

The circuit package 400 is provided with the connection terminal 412 inorder to supply electric power for operating the embedded air flowsensing portion 602 or the processing unit 604 and output the flow ratemeasurement value or the temperature measurement value. In addition, aterminal 414 is provided in order to inspect whether or not the circuitpackage 400 is appropriately operated, or whether or not an abnormalityis generated in a circuit component or connection thereof. In thisembodiment, the circuit package 400 is formed by performing transfermolding for the air flow sensing portion 602 or the processing unit 604using a thermosetting resin through the first resin molding process. Byperforming the transfer molding, it is possible to improve dimensionalaccuracy of the circuit package 400. However, in the transfer moldingprocess, since a high pressure resin is pressed into the inside of thesealed die where the air flow sensing portion 602 or the processing unit604 is embedded, it is preferable to inspect whether or not there is adefect in the air flow sensing portion 602 or the processing unit 604and such a wiring relationship for the obtained circuit package 400. Inthis embodiment, an inspection terminal 414 is provided, and inspectionis performed for each of the produced circuit packages 400. Since theinspection terminal 414 is not used for measurement, the terminal 414 isnot connected to the inner socket of external terminal 361 as describedabove. In addition, each connection terminal 412 is provided with acurved portion 416 in order to increase a mechanical elastic force. Ifthe mechanical elastic force is provided in each connection terminal412, it is possible to absorb a stress caused by a difference of thethermal expansion coefficient between the resin of the first resinmolding process and the resin of the second resin molding process. Thatis, each connection terminal 412 is influenced by thermal expansioncaused by the first resin molding process, and the inner socket ofexternal terminal 361 connected to each connection terminal 412 isinfluenced by the resin of the second resin molding process. Therefore,it is possible to absorb generation of a stress caused by the differenceof the resin.

8.4 Another Embodiment of Housing 302 Configuring Thermal Flow Meter 300

FIG. 21 illustrates another embodiment of the housing 302 whichconfigures the thermal flow meter 300. The same reference numeralsindicate the same configuration and the same functional effects areachieved, and thus the descriptions thereof will be omitted. The housing302 includes a first housing 338 having the bypass passage trench and asecond housing 337 positioned on a side near the flange 312. An airpassage 327 is molded between the first housing 338 and the secondhousing 337. The front cover 303 illustrated in FIG. 2 is provided inthe surface of the housing 302, and the rear cover 304 illustrated inFIG. 3 is provided in the rear surface of the housing 302. The inletport 343 illustrated in FIG. 2 is formed in the front cover 303 and therear cover 304.

The first housing 338 and the second housing 337 is connected to eachother by the circuit package 400 and also connected to each other by thefront cover 303 and the rear cover 304. In the embodiment illustrated inFIG. 21, while the first housing 338 and the second housing 337 iscompletely separated by the air passage 327, the second housing 337 andthe first housing 338 may be not completely separated but connected onthe outlet port side which is opposite to the inlet port. In this case,it is preferable that the opening be provided in the front cover 303 orthe rear cover 304 in order to guide the measurement target gas 30received from the inlet port to the main passage 124.

The air passage 327 is formed long, and thus the measurement target gas30 guided from the inlet port 343 flows vigorously. Therefore, thetemperature of the measurement target gas 30 can be measured by thetemperature detecting portion 452 with high accuracy. In addition, thecircuit package 400 can be cooled by the measurement target gas 30flowing through the air passage 327, and the influence of the heat fromthe wall surface of the main passage 124 to the air flow sensing portionin the inside of the heat transfer surface exposing portion 436 providedin the fixation surface 432 can be reduced. Therefore, the measurementaccuracy is also improved.

8.5 Still Another Embodiment of Housing 302 Configuring Thermal FlowMeter 300

FIG. 22 illustrates still another embodiment of the thermal flow meter300. The same reference numerals indicate the same configuration and thesame functional effects are achieved, and thus the detailed descriptionsthereof will not be repeated. The measuring portion 310 is originallyformed longer than the shape of FIG. 22, the structure in the vicinityof the flange 312 is similar to that of FIG. 5 or 6, and thus theillustration and the description there of will be omitted. Thisembodiment is different from the embodiment described above in that theprotrusion 424 of the circuit package body 422 in FIGS. 5 and 6protrudes toward the upstream side of the flow of the measurement targetgas 30, but the protrusion 424 protrudes to the center of the mainpassage 124 in FIG. 22. Further, the shape of the bypass passage isgiven as merely exemplary, and may be differently formed. In thisembodiment, the protrusion 424 protrudes exceedingly to the portion ofthe bypass passage trench on frontside 332 of the housing 302 formingthe bypass passage, the temperature detecting portion 452 provided inthe leading end portion of at least the protrusion 424 protrudes to theoutside from the housing 302.

A bypass passage trench 328 is formed by two walls (a passage wall 396and a passage wall 397). In addition, in the embodiment, the front cover303 and the rear cover 304 are provided on both sides of the housing302, so that the bypass passage trench 328 forms the bypass passage, andthe inlet port 350 and the outlet port 352 are formed. In the bypasspassage trench 328, the above-mentioned measurement surface 430 isprovided, and the measurement surface 430 includes the heat transfersurface exposing portion 436, so that the speed of the measurementtarget gas 30 flowing through the bypass passage trench 328 is measured.

When the front cover 303 and the rear cover 304 are provided in thehousing 302 illustrated in FIG. 22, the side surface of the protrusion424 is covered by a cover end 339 (the end portion depicted by thedotted line in the center direction of the main passage 124) of eachcover. However, since the center portion of the main passage 124 of thepassage wall 397 is opened, the measurement target gas 30 flows alongthe passage wall 397 and abuts on the temperature detecting portion 452.With such a structure, the protrusion 424 and the temperature detectingportion 452 are protected. In addition, since the bypass passage trench328 is formed such that the measurement surface 430 is narrow comparedto the inlet port and the outlet port, the flow rate is increased inthis portion, and the measurement accuracy of the flow rate is improved.The passage wall 397 is hollowed toward the inside in a protrusionportion to the outside (that is, toward the wall surface of the mainpassage 124) of the temperature detecting portion 452 compared to theoutlet port or the inlet port. The temperature detecting portion 452protrudes to the outside in the hollowed portion. With such a structure,the temperature detecting portion 452 of the protrusion 424 is protectedby not only the covers on the both sides, but also the inlet port of thepassage wall 397, the outlet port, or both of them.

The neck portion of the protrusion 424 protruding from the circuitpackage body 422 of the circuit package 400 is covered by the resinforming the bypass passage trench 328. For this reason, the circuitpackage body 422 and the protrusion 424 is mechanically protected by theresin of the housing 302. Furthermore, an effect that the circuitpackage 400 is securely fixed to the housing 302 can be obtained.

8.6 Another Embodiment of Temperature Detecting Portion 452 ofProtrusion 424

FIG. 23 illustrates another embodiment relating to the temperaturedetecting portion 452 of the protrusion 424. In the embodiment describedwith reference to FIG. 11, 15, 21, or 22, when the protrusion 424 isproduced through the first resin molding process, the temperaturedetecting portion 452 is covered by the resin used in the first resinmolding process. In the heat transfer surface exposing portion 436provided in the measurement surface 430, the heat transfer surfaceexposing portion 436 is not covered by the resin in the first resinmolding process in order to improve the measurement sensitivity of theflow rate. Similarly, since the molding is performed not to cover thetemperature detecting portion 452 of the leading end portion of theprotrusion 424 with the resin in the first resin molding process, it ispossible to improve the measurement accuracy of the temperaturedetecting portion 452. Since the temperature detecting portion 452 isnot covered by the resin, a hollow 454 is molded by the resin of thetemperature detecting portion 452. In the portion of the hollow 454, thetemperature detection element 518 described with reference to FIG. 12can abut on the measurement target gas 30 in an almost-directlyapproaching state, the measurement sensitivity is improved, and themeasurement accuracy is improved. Further, the same reference numeralsas those in the other drawings represent the same configurations and thesame functional effects are obtained, so that the redundant descriptionsthereof are omitted.

INDUSTRIAL AVAILABILITY

The present invention is applicable to a measurement apparatus formeasuring a gas flow rate as described above.

REFERENCE SIGNS LIST

-   300 thermal flow meter-   302 housing-   303 front cover-   304 rear cover-   305 external connector-   306 external terminal-   307 calibration terminal-   310 measuring portion-   320 terminal connector-   327 air passage-   332 bypass passage trench on frontside-   334 bypass passage trench on backside-   337 first housing-   338 second housing-   356,358 protrusion-   359 resin portion-   361 inner socket of external terminal-   365 the link portion-   372, 374 fixing portion-   400 circuit package-   412 connection terminal-   414 terminal-   422 circuit package body-   424 protrusion-   430 measurement surface-   432, 434 fixation surface-   436 heat transfer surface exposing portion-   438 opening-   452 temperature detecting portion-   590 pressed fitting hole-   594, 596 slope portion-   601 flow rate detection circuit-   602 air flow sensing portion-   604 processing unit-   608 heat generator-   640 heating control bridge-   650 bridge circuit of air flow sensing-   672 diaphragm

1. A thermal flow meter comprising: a bypass passage into which ameasurement target gas flowing through a main passage flows; a circuitpackage which includes an air flow sensing portion for measuring a flowrate by performing heat transfer with the measurement target gas flowingthrough the bypass passage, a processing unit for controlling the airflow sensing portion, and a temperature detecting portion including atemperature detection element for detecting a temperature of themeasurement target gas; and a case which includes an external terminalfor outputting an electric signal representing the flow rate and anelectric signal representing a temperature of the measurement target gasand supports the circuit package, wherein the case includes a resinhousing which supports the circuit package, the circuit package includesa circuit package body that is molded by a resin and the circuit packageis configured to envelope the processing unit and the temperaturedetecting portion with the resin, the circuit package includes aprotrusion protruding to the main passage by penetrating through thewall of the bypass passage, and the temperature detection element isburied in the protrusion, and at least a leading end portion of theprotrusion is exposed in the main passage.
 2. The thermal flow meteraccording to claim 1, wherein the circuit package is molded with a firstresin, the resin housing includes the bypass passage, a flange, an outerwall, and a fixing portion for fixing the circuit package, the bypasspassage, the flange, the outer wall, and the fixing portion areintegrally formed with a second resin forming the resin housing which isdifferent from the first resin.
 3. The thermal flow meter according toclaim 1, wherein the circuit package is molded with a first resin, theresin housing includes the bypass passage, a flange, and an outer wall,the bypass passage, the flange, and the outer wall are integrally formedwith a second resin forming the resin housing which is different fromthe first resin, and the circuit package is fixed by being covered by aportion of the outer wall.
 4. The thermal flow meter according to claim1, further comprising: a cover disposed outside of the protrusion. 5.The thermal flow meter according to claim 4, wherein a front cover and aback cover are provided on both sides of the leading end portion of theprotrusion, and an opening for flowing the measurement target gas isformed by each of the covers.
 6. The thermal flow meter according toclaim 1, wherein the protrusion includes internally a lead, and thetemperature detection element is electrically connected to the lead inthe leading end portion of the protrusion.
 7. The thermal flow meteraccording to claim 6, wherein the protrusion includes internally a firstlead connected to the temperature detection element, a second lead formaking electrical connection with an electric circuit in the circuitpackage body, and a connection line which is provided between the firstlead and the second lead in order to electrically connect the first leadand the second lead.
 8. The thermal flow meter according to claim 1,wherein a hollow is provided in the resin enveloping the temperaturedetecting element.
 9. The thermal flow meter according to claim 1,wherein the leading end portion of the protrusion protrudes to adirection of a center of the main passage.
 10. The thermal flow meteraccording to claim 1, wherein the neck portion of the protrusion isfixed to the resin housing by the wall of the bypass passage.
 11. Thethermal flow meter according to claim 1, wherein the wall of the bypasspassage is hollowed toward the wall surface of the main passage so thatthe width of the bypass passage at the point where the protrusionpenetrates through the wall of the bypass passage is narrower than thatof the outlet port or the inlet port of the bypass passage.
 12. Thethermal flow meter according to claim 1, wherein a front cover and aback cover are provided on both sides of the leading end portion of theprotrusion, and an outside of the bypass passage is opened to the mainpassage.